In order for S&W to do an M&P in 10mm they would have to build a frame specifically for the 10.

If they attempted to modify the existing 45 M&P it wouldn't work.

If they introduced a beefier frame designed from the ground up, with reinforced internals and a 22lb spring (minimum), I would sign up in a heart beat!

10mm shooters want a gun that can withstand a steady diet of true 10mm loads.