Mmmmm....WANT THIS GAME TYPE
A better way to solve the "no-rejoining" problem is to use the CS method - when you join you have to wait until the start of the next round, since you can only spawn at the start of the round.
As for the campers, well, force seeing is one solution as people have mentioned, but did you ever have that problem with UT? Not significantly I'm sure. It can be dealt with (if they do it too often then people could just vote them off in the next round).
Obviously, private duels may need to be disabled for this game, and you'll have to put up with people jumping you suddenly. I'd love to play this game type. A LOT.