The Firefly is at the top of ww2 tank technology, therefore another tank of ANY sort would only introduce yet another easily consumable prey animal to the game...
WAIT, I LOVE Firefly's!!!
In that case, BRING ON THE PANTHER!

Seriously, the ground game has been turn'd on its head..., and will remain so until some sort of reality is reintroduced in the form of Shermans that take realistic damage.
Im honest when I say any more Uber German (or of any nationality for that matter) tanks would be a waste when the Firefly is so strong.
It's not that I wouldnt love to drive somthing new..., it's just that any introduction seems pointless considering that further historical heavywhieghts would be overmatched in the face of an American tank that can survive multiple hits in its ammo storage by 88mm's.
The "Game" has a long way to go yet..., its surprising that the developers havent realised this yet...