Technically that formation isn't a wishbone. True wishbone is FB behind QB and HB's spilt behind the FB. Green Bay is splitting a TE and FB behind the QB and putting the HB deep in the backfield.
But it's a great formation, you get the lead block from the FB, a guard can pull and the TE can easily stop backside pursuit. Lets the HB be patient while the blocks develop.
IMHO, McCarthy is proving to be a very solid game planner. I like a lot of the new looks and plays they use - e.g., putting Jennings in the TE spot against a LB in the KC game... and having the patience to keep that set under wraps until a key point in the game. Good stuff.