We're putting the touches on v3.8. From here on out, a lot of our effort is going to be on features that improve the game experience, polish and usability. They're not sexy features but they're much needed imo.
Starting with 3.6, we began work on improving the modding experience. This is something that's been being further developed in 3.8 and will get more attention after as we try to "unify" the experience further so that people can eventually pass around mods and know they'll "just work".
We still have the general challenge in that you have Crusade and "base" GalCiv III v1.x. Crusade changes the economic system to a citizen based system so that's a big challenge in reconciling in terms of mods.
There won't be any more expansions for GalCiv III. Future gameplay improvements will be made to the Cruade base (i.e. as long as you have Crusade these will work). But we do have new DLC coming over the coming year.
If you have any questions, feel free to ask them here. Cheers!