We've already build special channel for searching league matches. It's #duo.league.. We were about to announce this "special" channel today in the evening.
Making people add their channel.. Well, oh, no. I remember, as I've participated in few leagues with my squad, it was really hard to find someone, since mostly they've posted some fake channel, or if they really had that channel, they were unavailable. Since then, I think the best way is to let searchers join channel, where they can start writing sentances like "numerite for dlctf" or so.