A cool idea! Thanks for the feedback, I've made sure to pass it along to the team.

I like the general idea a lot.  To expand on it, why not allow players to create fleets, even if they don't have any ships yet?  For example, you could start by going into something called "Fleet Management."  From there you can see any existing fleets, create a new fleet, or disband an existing fleet.  When you click on a ship or a group of ships, you can add them to any existing fleet.  (If they were previously part of another fleet, then this will re-assign the ship to the new fleet.)

If you select a fleet, you can specify the "target composition" which is essentially the blueprint and decide whether or not to auto-replenish the fleet to that target if it should lose ships below the target due to attrition during a battle.  You can also give the selected fleet commands such as "Move to this location" or "Attack this ship."  Having the ability to explicitly select the fleet and give it orders solves an issue with the blueprint approach on its own where it might be difficult to prevent the replenished ships from going to their doom against an overwhelming force if all of the existing ships in the original fleet have been destroyed.  It also makes it clear when you are giving orders to all ships in the fleet rather than just a specific ship.  If you select a ship or ships in the UI, you are giving orders to the selected group of ships independent of any fleet they may belong to.  If you give new orders to a fleet, the new orders will replace any previous orders the ships in the fleet have.   

I have't played Stellaris, so I'm not sure how similar it would be.  I am a software engineer, so when I read the original idea, I saw that there would be some issues that would need to be worked out in order for it to work.  Among those were things like once you have set up a fleet with the proposed mechanism, how would you give orders to the fleet going forward?  If you give orders to an individual ship in the fleet, does that change the orders of the fleet itself?  If the entire fleet is destroyed, how do you change its orders or set a new waypoint for the fleet to re-assemble?  

Thinking through those kinds of issues is what led me down the path of thinking that there would need to be an ability to explicitly create, select, edit, and disband fleets.  (CRUD - Create, Read, Update, Delete.)  The details of how to perform those operations through the UI could be done several ways, but the fleet feature wouldn't feel complete if all of those operations aren't available in some form.

SINS 1 basically had pre-assigned slots for a few fleets/groups that you can assign using Control-1, Control-2, etc...  That essentially limitted fleets to the number of numbers on the keyboard.  Also, a ship that is already in a fleet could be part of the selection when another fleet is created, resulting in a "shared" ship.  I see this as being somewhat messy.  If you have created a blueprint on 2 fleets where 8 of the ships overlap, and one of the "shared" ships is destroyed, do you build a replacement of that vessel type for each fleet, or do you build a single ship that is once again shared between the two of them?  If all of the ships in a fleet have been destroyed, how to determine which factories should generate the replacements and where they should rally?  Or would complete destruction of a fleet mean that the fleet no longer exists and shouldn't be replenished?

I really like the idea of auto-replenishment, so I would like to see a solution.  I just think it is more complicated than adding a button to tell a fleet to maintain the blueprint of its current composition.  I think it can work, but every way I've thought of to solve the issues so far involves adding functionality to specifically manage fleets.  If you have fleet management, you can specify the target composition of each fleet (blueprint), toggle if it should auto-replenish or not, give instructions to the fleet, etc... 

Some of the more esoteric concerns can be addressed through fleet management as well.  For example, you could specify the priority of which ships should be rebuilt first based on available resources and factories, that would include setting conditions that must be met for replenishment (specify maximum # of phase jumps away a factory can be from the current target location of the fleet, minimum resources that must be on hand before auto-build will kick in, etc...)  In fact, fleet management could even allow build priority to be set between fleets so that the game will know how to resolve a conflict between auto replenishing ships for fleet 1 versus fleet 2 when there are insufficient resources to build the requested ships for all of them at the same time.

This would potentially mean not allowing factories to be part of fleets anymore as the assumption would be that fleets will commission factories to build the ships that they need based on cost, proximity, and relative priority.  That would remove the need to worry about micro-managing where ships are built just like we don't micro-manage which labs are currently performing research.  (Which would be more relevent if my suggstion about research parallelism is used.)

The introduction of delayed spending doesn't exist in SINS right now.  When you queue up orders, there is no ambiguity as to what you want to pay for, when you want to pay for it, and where you want to spend it.  Auto replenishment means ceding at least some control to the game to make some of these decisions for you. 

Possible issues to consider:

1. What happens if you don't have the resources to order a build of the replacement ship at the time it is destroyed?  It can't be added to a build queue since all ships in a build queue are paid for.  If we allow unpaid ships into a build queue, then when does it get paid for?  (Allowing unpaid ships into a build queue would dramatically alter the character and strategy of the game.  Once you have that, the argument can be made that you should be allowed to queue builds any time you want even if you don't have the resources since they will start building once you do have the resources.  A change like that would dramatically alter the game's current dynamics.  It might work, but I don't think you intended a change to such a fundamental aspect of the game.)

2. Where do the build orders for the replacements get queued up?  Assuming that the game implements some type of automatic build location optimization algorithm that takes distance, time to build, and other factors into consideration, does the player have any ability to influence those decisions?  For example, can I tell it to calculate pathing costs based on a rule that the newly built ship(s) must stay in friendly territory until the last jump needed to join with the main fleet?  Can I specify if path costs should include projected orbital motion?  (For short build queues, orbital motion may not matter much, but if we are auto-building very long queues, then orbital motion becomes more of a concern.)

3. Do build locations get re-optimized if the player builds additional factories that didn't exist at the time the original ship to be replaced was destroyed?  (This could happen if enough ships are destroyed to create sufficiently long build queues for a factory to get built in less time than is required to finish building all of the replacement craft.)  What about if one of the factories building replacements is destroyed?  Do the ships get re-allocated to other factories that are still operational?  If so, do the reallocated build requests move to the end of the line, or does the order get shuffled to try to maintain the same overall order of build as the ships they are being built to replace were destroyed in?

4. How do auto-generated build queue orders interact with player decisions if they click on one of the factories building auto-replacements?  For example, if the player cancels the build of a replacement ship at a specific factory, does that mean that they are removing that ship from the blue print, or should the game simply assume that means that it needs to auto-pick a different factory for the build of that specific ship?

I could keep bringing up other potentially unintended consequences of this change, but after having given it some thought, I think I have a potential solution that is in keeping with the current SINS philosophy/style.  The simplest solution I see that avoids most of the unintended consequences is to allow a fleet composition to be specified, and provide a button called something like "Replenish Group" that will show the cost to build all of the ships that are needed to fill in anything that is missing compared to the target configuration.  It would also allow you to choose which gravity wells with available factories should be used for a replenishment.  If you have the money (and the supply) to build everything needed to reach your target configuration, then you can click the button. Otherwise, you have to change your target to something that fits within the constraints before you can click the button.  (Factory types at the participating gravity wells would be taken into consideration as well to determine if you can click to replenish.)

With this solution, resources are decremented at the time the user clicks to spend them, so there are no unintended consequences due to automated spending concerns. This also leaves the player very much in control of what will be built, and where it will be built, so very little is ceded in terms of control.  Basically, to me, this feels more like the natural way for a SINS game to eliminate the where's Waldo tedium brought up at the beginning of this thread.