Well, the 7.62 NATO came about because the .30-06's length made is a bit fussy in cycling a full auto weapon, so a .270 WIN, being a necked down .30-06 is out of consideration. A necked down 7.62 NATO(.308 WIN)to .270 seems viable, but the cases are still as fat as the .30-06(same problem with the beloved .243 WIN), limiting on board ammo considerably, which I'm sure brought about some of the thinking that gave us the 5.56mm NATO.
So....we argue long and hard over the compromise of case size(powder capacity), bullet size(where we should be concerned about sectional density mostly), and velocity(for best trajectory).
Then....we need a weapon that will reliably dispense this fancy new round, we need it to NOT be fragile in any way, and we need it to be compact and lightweight. Oh, yeah, we need it to be managable for women.
Did I leave anything out?
"Did I leave anything out?"
No. You're absolutely right. Things are perfect the way they are and are in no need of modification or thinking "outside the box".