The following is simply an observation: The US Army desperately needs to upgrade the weapons systems of the infantryman as well as any sidearm carried by support personnel and officers.
The M16/M4 series has had it's day and so has the 5.56mm cartridge. The basic platform is okay as it goes as can be seen in the somewhat derivative H&K 416, which is still a huge improvement in the reliability factor. But the 5.56 isn't doing the job. Perhaps the 6.8mm would be a better choice. If the operations anticipated in future war will be engagements at less than 300 meters than perhaps one answer could be found in the .300 "Whisper." Perhaps not, but it's a suggestion. Maybe the 300 Whisper could be a specialty cartridge for SOF folks but then they'd only fall victim to those same bottom feeding bureaucrats. In any case, there must be trials to discern what might be superior and then to seize that information and actually act upon it.
I also think that suppressor technology can be advanced to the point that a suppressor can be attached to all battle rifles lowering noise signature and flash. Probably make BRM (Basic Rifle Marksmanship) easier to teach, too. But that's a side issue and I certainly don't have the knowledge to speak with authority.
Speaking of sidearms, now: IF we weren't constrained by the Hague accords on ammunition and could employ JHPs with our 9mm sidearms they'd probably be fine since technology makes the expansion properties of the 9mm and the 45ACP nearly identical while still allowing for the single most important factor in a handgun encounter at any range: SHOT PLACEMENT. Still if we're stuck with BALL ammo then the 9mm becomes wholly inadequate. Cross sectional density and velocity almost dictate the tried and historically proven 45 ACP, but NOT the 1911 platform. I know a lot of folks will consider that heresy, but I think that the H&K 45 should be the sidearm of the future armed forces. Just MHO.
For a sidearm, I’d vote for something along the lines of a sig 250 modular setup. For caliber, a 10mm.