With one post, dalek mightily shuts this thread down. =P Like he said, not enough games. I don't even think there are more than 10 multiplayer games on this site.
Seeing as AG3 is already in open beta, there is no point in implementing anything new into AG2.
In AG3, there will be a more advanced tagging system. "Multiplayer" is more than likely going to be a tag in AG3, but there probably won't be enough multiplayer games for them to have their own section anytime soon.