I read the linked stories and pulled up an old article on the M855A1 ammo. Basically, it uses a green (lead free) projectile that, because of longer projectile length, increases both chamber and port pressures. Also uses a powder that reduces copper fouling (which, if memory on load data is correct, also has some pressure problems).
Buried in the first story is a partial explanation of some things. The Army decided to use a bullet in all their 5.56mm ammo (62 gr) because it was better suited to the mission of the M249/SAW. The rifling twist of the SAW had to be 1-7 due to issues with the tracer ammo. For no technical reason, the rifling twist of the M16A2 & M4 were also changed to 1-7. Sometimes, the military insistence on uniformity makes no sense at all-although it might have saved the barrel blank makers a few cents per barrel in not needed multiple mandrels for barrel forming.
Moving the gas port (mid length) would solve a lot of problems with high port pressure and the problems that can result from it. However, that would make the M203 require a re-design or be scrapped in favor of something like the old M79. I'm not sure what the comparative rates of fire are, but the M79 was a good item. Matter of fact, the SEALs seem to use it quite a bit.
I do, very faintly, recall a press release some time back from FN about their SCAR-L getting DOD clearance for purchase. However, FN also noted that their were many military needs and no one should expect a wholesale change over to the SCAR.
I expect the DOD is correct in deciding that given their current budget issues-including the need to be able to destroy the planet in an ecologically correct manner-mean they'll stick with the AR platform until a truly significant advance happens. Maybe a man portable pulsed laser in the 40 gigawatt range.