Well, the US government has recently been experimenting with the newly-developed Remington 6.8 SPC, which stands for Special Purpose Cartridge, if I am not mistaken. They have been using the M4/AR as a platform for tests. This is roughly a .270 caliber bullet in a necked down .30 Remington shell. So far, it has shown to be more powerful with a higher sectional density than the 5.56, with increased muzzle energy and flatter trajectory. Now this is for assault rifles and eventually probably belt-fed squad automatic weapons, and will probably not be introduced as a sniper rifle caliber. But concerning sniper calibers, I personally don't think we'll need to get any more powerful. The .338 Lapua, .50 BMG and new .408 CheyTac will probably be able to be made to shoot through most anything the enemy could be trying to protect themselves with. But thats just my opinion. And as you said, I do not think we'll be fighting anyone with technology as great as ours in the near future. I doubt Iraq, Afghanistan, etc will ever be able to afford to produce it on a widescale basis for their troops.