Interesting question.
I would place my bet on Polymer framed, interchangable griped, striker fired, external safety pistol with a barrel length of atleast 4 inches.
For ammo, if NATO is not the concern then .45 acp. If NATO is a concern then we will stay with the 9mm or all swap to the 5.7 round with an FN or HK platform.
If we stay with the 9mm then the M9 will be here for awhile longer. If not the M9, my bet is on something like the SW XD or MP platform, or something similar from FN or HK.
