I'm not really sure to be honest. For a start dungeons are rather rewarding and if they rewarded rep they would almost certainly have to factor that in to the gating of the rep. Secondly that limits what dungeons or beast tribes they can add because there are quite a few cases where that doesn't work. For example, what dungeon would give Gnath rep? Or Sylph rep? We aren't going to get more dungeons than we already do, at least for now. It would mean that new dungeons would almost always be limited to being related to whatever beast tribe was the lastest to get a rep.