It already exists, it's called the 757. lol
Joking aside, buff is a terrible transport choice, for a ton of reasons that are self-evident and won't rehash for brevity. There's a reason transport category aircraft are designed and dimensioned specifically how you see them, compared to pencil-necked, teenager-limbed contraptions like the buff.
For the record, the reason the Buff endures in the usaf inventory is not because of some old Boeing "
they don't make em like they used to" baby boomer americana bull poop nostalgia. It's merely because 1) it's paid off and the tooling long ago wrecked 2) the Hs were babied and spared action during the cold war by mission assignment proxy and 3) the mission has looong ago been diluted down to that of permissive standoff missile-only truck. A mission a 757 with a CSRL/1760 bay cavity and refueling plumbing could accomplish in more comfort and to higher crew morale. Digressing.
Oh, fun RUMINT. Over on the .mil pro site, someone posted a redacted memo as to the re-engine program being summarily snuffed by HAF. Taking fat amy to dinner and bang is a spendy task, cuts have to be made.