I'd be very cautious about implementing a system that essentially... sounds like a configuration management system (including templating, post-hook actions, etc.).

Where do you expect us to be needing this?

Pybal is the first suspect, but we need something that can change file state reliably upon etcd state change fleet-wide. Another example would be haproxy configurations for databases (for example)

Confd was supposed to be exactly this, but in my testing it has shown some inherent limitations that I wanted to try to overcome. We could limit scope of this and just make it act like the consul agent (just return values pertaining to the current node upon request), but as long as we use it just to configure /state/ (like we do with confd) it would not step on puppet's toes.

So should I not bother with https://gerrit.wikimedia.org/r/#/c/225649/ ?

@ori not at all, if we do integrate pybal directly this is just a lower priority task.