I'm not experienced haskeller, but I've started to work on augeas property for propellor. I've created a separate repo for it: https://github.com/paluh/propellor-augeas. I will try to rewrite some existing properties on top of this and add some new. It is in a really early stage, but it works.
I think that it will be a lot easier to work on propellor core properties and features, if it will be separated lib without any "spinning" abilities. Currently when I'm trying to read your or my commits history, there is a lot of "propellor spin" commits, without any sensible comment. In addition, it is hard to merge any changes to your repo - I can't just send you pull request. In case of such a broad project as propellor, I think that it will be beneficial to facilitate cooperation and to separate deployment mechanics from core configuration management parts. What do you think about extracting pure library from existing project?
This seems like it would be a useful addition to propellor.
As to commits made by propellor --spin during development, those typically involve changes to my own configuration, or minor changes, but sometimes other changes slip into one of those commits during the press of sysadmin events. I doh't see how those would prevent you from sending patches though.
I'm generally happy to accept new modules into propellor. However, this one is problimatic since it adds several new dependencies. I want to keep propellor's dependencies minimal.
It could be integrated behind a flag in propellor.cabal, but then I'd need to worry about testing it (or not testing it) for integration when there are changes.
So, maybe this works better as an addon module? A propellor user could then add it to their config.hs. Only problem I see is, it currently depends on propellor, so a user can't modify their propellor.cabal to depend on it. So you'd have to use propellor as a library.