Okay so, while looking through old suggestions I found this one and - obviously, limited-count exits have already been done. I'm not really sure what "walker only" would do (unless this means as in eg. a lemming building past it would ignore it but walkers following him would exit), nor "use as unlock switch", but there will not be any kind of exit that allows (let alone exclusively allows) zombies - use neutrals if you need that. In all fairness, neutrals did not exist yet when that post was made, but it's an option now.
I'm not convinced permanent-skill-only exits are worthwhile, especially when you could likely place an exit such that the permanent skill in question is required to access it. Disarmer could be a bit tricky to do this with, but the rest should be no problem, and I don't see that one edge case as being worth implementing the feature for.
As such - I'm closing this topic.