Ah, sounds like you've got it exactly. Religion system as a major thing, same as Vaults, as would Achievements/Conducts, Branches, any sort of eventual Tile or DoomRL-level Sound support, etc. Pretty much the perks of the game that are the things that'll get packed with content as time rolls on.
Each one of these you get knocked out brings the game that much closer to growing the playerbase, as each nifty bullet points stands to attract yet more people, whom will then also hopefully contribute good notions to flesh things out moreso.