Yeah, and compiling all this to a human-readable summary will definitely be impossible in all circumstances. I think policy might be best indicated by a combination of common, standard limitations (or rules, sure), and a human-readable description. Eventually, common configurations might be compiled into simple tags, like "paid inbox" or "fresh pubkeys". If a relay advertises that it's good for a given use case, they don't have to prove it and might not work well, but users and clients could at least make more intellligent guesses. 

 Human readable description makes sense.