With the response being as it is in Xonotic and over at Warsow as far as I can see, I believe we'd be better off for a start (!) with making it a free for all deathmatch session with a couple of matches per game on a given date, and calculate overall rankings among the people that participated in all matches afterwards. We might get enough players to fill a deathmatch server and after all in deathmatch it's far less about map knowledge and physics exploits than in duel, where a "home bonus" will easily result in total domination (I couldn't even IMAGINE myself scoring a frag against anyone at least half way competitive in quakeworld on hub). I think such a tournament would be far easier to pull off and would also be more attractive to players, since chances are you can actually score at least some frags in a deathmatch if you have some solid basic fps skills.
Team based competition sounds sort of cool, but then again I fear it would rather deepen the divide between player communities in the end. Obviously we'd mostly have teams coming entirely from ONE game community, which means we'd then have direct rivalries between the game communities. And I don't trust in the spirit of sportsmanship to prevent conflicts resulting from these rivalries. IMHO team based competition would ONLY make sense if we would build up teams consisting of players from each game community, but how to set THAT up reliably?
If we are going to make it a duel cup despite the concerns I raised above, I'd vote for Fuse, Stormkeep and SilentSiege as map pool, agree to Smilecythe here.