Greenhat--
None. That's part of the problem: every solution that's been come up with, comes with its own suite of new problems. As such, I'd bet that average troops going from M4 to M14 (or similar variant) will come up with a bunch of new gripes and bitches, including too much recoil, too much weight... one of the flaws I can see with my/NDD's tentative solution is that, with 'average' troops, or even normal infantry, the problems will be enough to offset the advantage we'd actually get out of the rifle system.
As such, I have my opinions on matters. But for solid solutions? I don't know. Hence, the looking for opinions.
--Dan