I'm in the process of adding shrines to the keeper mode. Here's how it will work initially.

There are about 5-7 randomly generated deities, which you may already know from adventure mode. Each deity is assigned a habitat and a few epithets, which you may find if you scroll to line 22 and 31 here: https://github.com/miki151/keeperrl/blob/master/pantheon.h (the epithets and habitats are work in progress)

You can now build shrines for any of the deities. In addition, you can build shrines for any  major creature that can be worshiped, which for now includes the dragons (which will be a lot stronger in the next release).

Your minions have a new task which is worshiping whomever you've built shrines for. Your standing with that god or creature obviously increases with the amount of worship, and you get benefits based on the epithets and habitat of a given god or in the case of dragon you may beg him not to attack you :). In addition, to stop you from building a shrine to every god, they have complicated social interactions (as every good pantheon), so you may anger them if you worship two gods that are enemies.

You'll also be able to sacrifice prisoners at the shrines.

Well, for now that's what I've come up with, and currently implementing. It's a simple system for now. Any comments or ideas are welcome.