The AP rounds that the military would have access to that we do not,they most certainly would penetrate armor, they were designed for it.
The FN fiveseven had 100% one shot stops when hit either center mass or headshot from the Ft. Hood shooter. The limb shots had severe tissue damage.
I believe if the army wants to think about the future of warfare, adopt the 5.7 or at least somebody do some extensive field testing.
Otherwise, the army cant have everything they want. They want a deadlier caliber, retain high capacity, and have it fit everyone's hands from Tinkerbell to Sasquatch. You cant have it all.
Assuming that we dont violate the no JHP rule, most logical option I see is the FNX-45, it wont fit the smaller hands, but neither will any double stack 45. It holds 15+1 of .45 is an accurate DA/SA pistol with a rail, currently available threaded barrel and the slide is milled for a red dot.
.357sig isnt more powerful enough to warrant an entire platform change. Army is too pussy to adopt 10mm. .40SW would be ok but you would have a 9mm sized gun with reduced capacity to hold the 40 and possibly have longterm reliability issues. What else is there caliber wise? I dont think they are gonna go back to revolvers.