I this was kinda addressed by the PLR vs. A/D CTf contest. With 2 game modes to play with things did not get boring until very late in the contest because of the extensions.
In other words if were to to have say Dustbowl vs. Gold rush (3 stage cp vs. 3 stage pl) I think people would be less bored.
I would like to see a 1-stage A/D contest. Maybe a contest for any A/D mode (CP or PL) the only requirements are that the map is only one stage and that red team must win by timelimit (defending). This opens up many gamemode possibilities that are somewhat comparable to each other for purposes of judging: Linear CP (Gorge/Artpass), A+B=C Style CP (Gravelpit, junction), and single stage payload (badwater, upward).
I like this idea.
Single stage A/D could also be Invade CTF, even.
I can't even fathom what a new mode that would work for tf2 would be.