I voted for everything
I like all of them. Maybe in any redstone contraptions you could see the redstone that makes it work to learn how to do it (just by looking of course). I know you don't actually need redstone in game but it's like learning how to camouflage. It's not NECESSARY, but it's a cool skill to have.
Parkouring would be really fun, and good practice. Right now in the lobby I have pretty much nothing to do and this would help.
For the free roam outside the city, that's not the best idea, but I like it anyways. Sometimes I might like a chance to explore that city over there
And in the combat area, it could have a bunch of chests full of swords. I know there would be the issue that someone could steal them all, but who cares. It's just the lobby. That way you could kill each other, and you would just respawn back in the lobby spot where you always spawn. It would be GREAT for practicing your team killing. It would also make the lobby more like a Training Centre like they had from the books.
Also, like Krasso said, it's not high priority. It's a good idea, but I doubt it will be implemented soon. I would say it will be done when the plugin is almost out of beta, and the devs and others have some spare time on their hands.