Amplitude Studios is one of the indie studios has definitely embraced the idea of ongoing development and fan feedback. Their Games2Gether system, early access launches, polls and ongoing, free addons make their games one to watch as a model going forward.
That however is a bit beside the point as their first 4x, Endless Space, has been announced to get its 7th free addon next week – Chronicles of the Lost. Chronicles will update both Disharmony (the expansion pack) and the vanilla version. With Disharmony they are improving some of the flaws that were in the expansion pack (which received mixed reviews), and also bug fixes for both it and the vanilla game.