"I would say 2v2 and 3v3 would be the best layout to start with. Any less and it's just like KoTH, any more and it's just like SDL."
Well.. KOTH isn't 1:1 at all (has more to do with predicting the way clumps of 1-5 player furballs will go), so a 1:1 division would definitely be interesting. IIRC there was an overlap in the AHDL and KOTH respective lifetimes. The SDL could be a separate division that's also displayed in that hypothetical lobby's standings billboard. I don't think these are mutually exclusive as far as Lobby display and official sanctioning goes.
Dunno if you mean my suggestion, on the monthly reset. The way I'd do it would be to have a monthly display of the top standings on the HTC home page, for all "divisions" (1:1, 2:2, SDL) like they do for scoring (regardless of the reset for that). There wouldn't have to be a reset for the dueling ladder divisions.