Hi,
this is actually more a question than a suggestion:
Why not give users (the lobby creator) the abbility to choose between Teamspeak3 AND Mumble?
I know that in the TF2 community mumble is very popular, but to be honest, TF2 is the ONLY community I know which favors Mumble over TS. I don't want to start a discussion about which is better, just want you to know that there are many people outthere who favor TS over Mumble, and forcing them to use Mumble might not be the best idea to widen your community.
For example ESL Verus system has a very good integration of Teamspeak.
cu
PS: Ofcourse I'm not suggesting to have BOTH at the same time, but I mean that the lobby leader can decide what he wants, TS or mumble everytime he/she starts a game.