Pros:
Hydras can retreat more quickly/micro easier?
5-6 Queens can transfuse your roaches or muta flock to keep your momentum and win more battles with good micro? High Hydra DPS and "high" roach armor suddenly seem like valid strategies vs T?
Queens are more useful in the late game?
Cons:
No more easy wins as Terran?
ZvZ gets weird?
Tons of mobile transfusing queens with a lot of starting energy suddenly become a huge problem for any army? (Solution: don't allow queens to transfuse queens?)
*It would also be nice to have a queen starting energy upgrade to further the transfusion idea. I really think queen anti-air would really complement a Z's midgame.