Except the AR platform lends itself to the DMR role unlike the M-14 so less money should theoretically need to be wasted on redesignating it. The M-21 was a bodge job of the M-14 was a bodge job of the M-1. There is nothing wrong with the M7's dad (Sig Spear LT).
80,000 psi should be ok for a DMR's lower round count. The issue is with it being brought to the M250 as well. I'm sure the parts are more durable, but the rifling is still going to get chewed up.
If the army wants increased range, lethality and effect against body armor without upending the entire logistics chain they should go with the 77gr. and the rifle a Sig Spear LT, but that wouldn't be flashy enough for the glamour kittens in procurement.