First the Medic, then Pyro, and now Mr. Heavy. Valve has announced
that the Heavy class is next in line for Team Fortress 2
class updates (i.e. new weapons and achievements). Additionally, Valve said it will "open up the process a little" in talking about how the update is designed. The goal of the update is to "make the Heavy more viable when he has no Medic to pair with" but in a manner that does not significantly change the Heavy's role in the game. We're interested to see how those ideas and constrants translate to new firepower.
[Thanks, Andrew R!]