Your idea does not seem to convince many players.
It is NOT a bad idea, but I think it needs to modification to it.
So your main problem is that there are not much parkour stages for regular players. What can happen is maybe players that have been on the server for a long time can get gifted a special rank in honourable of their royalty to the server. That rank can unlock special NON donator parkour stages untitled to only for those with the rank. Since it is a honourable rank to get, not even donators will be able to access those parkour stages as a 'perk', unless they receive the rank, obviously.
I have also prepared a second simple idea, in case some people didn't like the first adjustment to the thread owner's idea. It is very simple, we can convince the build team to make new parkour levels. Let's hope for it.