To be clear, the issue in the first place is that there isn't much left over strength margin in the AR15 bolt. Practically every other design has a proper 2X-3X (or more) margin, but the AR was so efficiently (read: lightly) designed for the specific 223 cartridge, t'aint no way to bump up the power much at all. No room to get wider in the case due to bolt strength, and even less room to get longer in the case due to the magwell.
For the 'most modular blah-blah-blah' ever devised, it really does have some fundamental limitations as far as chamberings go (luckily and/or coincidentally, there's a veritable cornucopia of cartridges at or below the AR's limit). I've always said that someone needs to blow out the front of the magwell & incorporate it into the upper, so longer cartridges capable of delivering more power at reasonable thrust levels may reach their potential from longer and/or larger bore barrels.
Even better would be a stronger bolt/extension design, but this would mean giving up the AR's exceptionally small unlocking cam angle (small due to very narrow, but more fragile lugs)
TCB