How could or should the 6.5 mm Grendel be improved?

[stanc]

I doubt that this will make much difference since the new loading will almost certainly match the exterior ballistics of the M80, otherwise they'd have to change all of the MG sights. And it will weigh just as much, and recoil just as hard.

The only significant difference between M80 and M80A1 performance is likely to be in hard-target penetration (and possibly soft-target effectiveness), but that doesn't affect the ballistic comparisons since these don't take bullet construction into account.

It is bad news in one respect though - the more money the US Army pours into new loadings for 7.62mm and 5.56mm, the more resistant they're likely to be to a change in calibre.

I'd say it's bad news in two respects: The resistance to change you noted, and improved terminal ballistics, which may or may not be matched even by a 6.5mm EPR. Otherwise, I agree with all of your comments.