First of all I'd like to drop down some words of appreciation for this post, since it makes me happy to finally see CubeCraftGames Parkour coming back after years of maintenance.
When it comes to Parkour, I'd like to have it just the way it used to be, but with the 1v1v1v1 duel mode. "The way it used to be" would be that Parkour gets 3-4 hubs, in which the chat is only visible for said hub, making it a community on its own. In that hub, you'd have the lobby as usual, with access to the different difficulties of Parkour, Easy, Medium, Hard, and whatever you'd like to add (Extreme, Adventure, etc.), and an NPC to show you a list of the parkours (Just so you can add parkours without the trouble of running out of rooms for signs.
The special thing about the Solo (Time Trial) version was, that you could see other players, and back then we used to race just like that on our own without fancy codes to restrict movement until a countdown happens. That way people got to play on their own, or simply got to duel without any further pressure.
Regarding the Dueling mode, I'd simple give it an NPC like the other modes, and give several maps with queues attached to them. That way people could see how many players are currently queued, and could tell when they're able to participate with just their friends.
That's really about all I have to say for Parkour, and I really hope that you'll take the time to go through our posts, as I do find it would be the fastest way of patching together a likable Parkour server again. I hope I won't be disappointed, of course!