I would like to see a Frontier version of Brawl. I think it would be a pretty spicy mix up for both formats... on one hand, Brawl would get to receive a much bigger card pool to play around with. On the other hand, Frontier could be tamed by reducing the consistency of having 4 card copies of all the best cards in the format.
Dunes of Zairo
SHANDALAR
Innistrad - The Darkest Night
~THE RAVNICAN CONSORTIUM~
A Community Set
Commander: Allies & Adversaries