It was simply an attempt to increase the anti-personnel potential of an M4 sized AR platform with the minimum amount of modification.
The original design request also required that the magazines be the same size and shape, so they would fit into the existing military issue mag pouches and vest pouches.
They eventually settled upon a case based upon the old 30 Remington. Prototypes were tried in 6.5mm (.264), 6,8mm (.270) and 7mm (.284).
The 6.5mm was found to have the best down range ballistics while the 7mm was found to impart the most damage to target medium. So, as in all things government, they settled on something in between.
From my 16 inch barreled Stag (1 in 10 twist, SPEC II chamber) I have consistently chronographed:
90 grain HP (2,850 to 2,900 fps.)
110 grain boat-tail (2,500 to 2,550 fps) 110 grain Accubonds work best
130 grain spitzer (2,200 to 2,250 fps)
A 110 grain .277 caliber Accubond with a B/C of .370, which leaves the 16 inch barrel at 2,550 will still be going 1,902 fps at 300 yards. So the 300 yard impact is about like being shot with a 30 carbine round at close range.
Within realistic combat range for a carbine sized weapon, the 6.8 SPC was a good idea. Plus at very close range, it offers more energy transfer (Hey stop that right now!) than a standard 5.56mm FMJ round.
However, you will not see ANY advancements if infantry weapons during the current political administration. Having dead or disadvantaged troops only advances the agenda of those currently in power.