The Paths to Power DLC is an incredible concept allowing players to explore the game's mechanics in a sort of different minigames. Although with so much potential, the Paths to Power DLC is still a bit lacking, so i'll leave some Scenario suggestions:

1. Defend The Homeworld Coop: the same concept but for 2 players.

2. Capture Points: 

 - On a star system inhabited by a less advanced civilization (like a type 1 incapable of colonizing other planets), players start from the homeworld but don't have time or resources to conquer/colonize and must instead vassalize (by defeating a garrison or expiring a timer) each planet for tribute/income.

 - Each vassal provides more income to pay for reinforcements, research, items from your homeworld. 

 - The player with the most vassals secures the most income but to avoid snowballing vassals will try to rebel and players must supress such rebellions. 

 - Players must split reenforcements into diferent fleets and strategize to vassalize planets and try to defeat rival players by taking control of the entire system or holding the most capture points for the longest time.

3. Convoy Escort: 

 - Having arrived at the star of an uncharted system, the player starts with a fleet and must escort convoys arriving at the star with specialized colonists to terraform the resource rich uninhabited planets on the outskirts of the system. 

 - This system is full of minor factions, raiders and uncolonizable gravity wells except for these rich uninhabited and unterraformed planets in the outer rim of the system.

 - The players start at the home planet with a base income for the war effort and must scout the system for these planets, send convoys and escorts to the star to colonize said planets, while using minor factions for safe passage, avoiding raider planets, destroying incoming raiders, converting ancient starbases, completing missions for resources and destroying enemy convoys.

 - To avoid snowballing players with the most planets may be targeted by more/larger raids.

4. Mercenary Missions: 

 - On an isolated star system, an empire (any TEC or Advent or Vasari Alliance) is being invaded by TEC Primacy, Advent Wrath or Vasari Exodus, who are seeking to nuke/plunder, convert or devour it's planets for resources.

 - The player is the commander of a fleet of mercenaries at the service of this empire and is given missions by the leaders such as defend worlds, escort colony frigates, protect a titan, destroy starbases, destroy fleets, capture derelicts, find artifacts, secure ancient starbases, scout wormholes/planets, etc. 

 - As the fleet commander the player can't colonize or manage planets. Instead, as missions are completed the player is given recognition with resources, exotics, ships, research upgrades, ship items, etc.. The player can however use such resources to call for reinforcements, build ship items or upgrade ancient starbases. 

 - The goal is to have several fleets to respond to simultaneous missions and different situations and hold of the invaders until reeinforcements arrive or a titan is built and eventually take the fight against the invaders with an epic final fight to take down the enemy Titan and remone enemy presence in the system. 

 - For multiplayer, have players be able to exchange resources and ships between each other and work together to complete as many missions as possible.

I recognise that the implementation of such scenarios requires delicate balancing at several levels and a lot of experimentation to make them fun. So my main suggestion is to provide modders/players with the tools to create scenarios or more costumizations options (number/types of stars/planets/wormholes/uncolonizable gravity wells, starting positions, etc.) and basically allow for an infinite source of minigames and experiences based on the game mechanics.