Automatic advertising is a horrible idea, IMO. Everyone would use it, because "there's no reason not to", even though that greatly increases the clutter. Also, if the number of users mattered, people would be doing dumb stuff like mostly leaving a room so that it's advertised more. The only way to make it somewhat work is to have it as an option, and give it an harsh decay rate (resetting every time a song is played) which is overridden by the advertising button. But with all those restrictions, I feel like there isn't much of a point.
Otherwise this sounds like a great idea for people who actually want to find a room to play in. It's obvious some people use #lobby as a sort of #AllLanguages channel, and those people will probably be upset, but I don't know if an #AllLanguages channel is something anyone would want to moderate. Maybe when Clans/Teams/Whatevers are finally added to the game, and they have their own chatrooms, that'll help some? Probably not, but I guess we can still hope.