I really like the idea of the arenas / specific pvp zones. This way there can also be official pvp tournaments and, if we wanted, things like spleef. I'm not entirely sure about the whole island toggle, though. It'd be a good donator perk to be honest. Something to make the really expensive donations worth it other than more pets and the ability to change the weather. That'd be so much rolling back and honestly is it worth all the effort? By that logic we should remove the worldguard on islands because, well, if someone gets griefed we'll just roll it back. Also, like, congrats on existing. If we're going to have arenas, we need to make them official and protected.
I suppose it would be a bit of extra work. I do like the idea of just having some of the server's more talented builders making some new sort of PvP arena, but the problem is getting the correct people working on the project. Some people are great at building buildings with great looks for example but they may not be able to make buildings that function very well for PvP. The former seem to be doing most projects on servers due to how nice their buildings look to the ownership of servers, which would be nice for spawns and the like, but they might not be capable of laying out their buildings in a way that functions well for a good PvP experience (spawn PvP looks average and doesn't play well so it would need to be someone who didn't make that).