solaristics wrote:
Thanks again.  My interest in  potential expansions/dlc is less in the addition of new factions, and  more in the development of the game mechanics.  It looks like at least  some of these in EL did this, so hopefully this will be an important  aspect of ES2 expanisons/dlc too.  

The way EL expansions (apart from smaller DLC) worked was that they introduced new gameplay mechanics that could be used by all old factions and a new faction that's specialized in the new mechanics. 

Espionage expansion added various spy actions, camouflaged units, pillaging mechanics and Forgotten with unique perma-invisibility units and their faction is better geared towards spy actions in general. Winter expansion added a new type of resource you could hoard through harvesting periodically refreshing nodes over the map, and a new exploration focused tall faction that could get and use the new resource or affect the global winter effects the easiest while simultaneously avoiding the negative global effects themselves. Sea expansion added naval combat, sea ruins and controllable sea fortresses that'd give free resources to factions controlling them and a new faction specialized in naval supremacy.

So when ES2 eventually gets its bigger expansions it's likely it'll be new gameplay mechanics + one new faction that excels at the new mechanics. However the first announced DLC for ES2 is supposedly a smaller one, kind of like EL's The Lost Tales DLC that merely added a bunch of quests tied to previous already existing minor races.

https://www.games2gether.com/endless-space-2/blogs/566-pick-the-last-faction-to-join-our-minor-faction-content-pack

As you may already know, we have tons of content planned for Endless Space 2, but we don't want to spoil you yet, so here's a little something to top you up until we reveal more...

That's why we have decided to give you the opportunity to add another minor faction, if that's the kind of thing you're into, with a vote! The faction will be the fourth to join an upcoming minor faction content pack. If you are familiar with Endless Legend, it will work kind of similarly to how we made The Lost Tales: something nice for those of you who want to inject a little extra life and lore into their game! We will give you more information in the months to come.

So probably few minor factions with their own assimilation and pop bonuses, plus hopefully more quests added to regular minor factions with unique rewards for completing them as well.