So, a STOL widebody transport with enough capacity to carry a tank or four (I'm thinking about 4x M551s or 4x M41s, not 4x M48/M60s, carried 2x2)?
I think the first challenge would be to have a mechanized airborne unit that needed full-sized tanks moved by air. That's a pretty uniquely Russian idea, though I'm sure the 82nd would love to have transport and fire support other than their boots. How's that line go again? "Too light to fight, too heavy to run"?
For that to work, I think this requirement would have to happen pretty early on before the C130 really dug in as THE tactical airlifter. Maybe if the engines had proved troublesome?
OR, this requirement would have needed to catch the C141 before the stretched -B models were developed, and a larger budget was available for fixing the "run out of volume before running out of weight capacity" issue.
The M41 Walker Bulldog is 3.2m wide and 5.8m long through the hull, so carrying them 2x2 would require a cargo bay at least 6.5m wide by at least 11.6m long (I'm assuming the guns are arranged to overlap the hulls of the tanks), and probably closer to 7m wide by 12m long. Cargo weight of 208klbs. That said, the US Army quickly decided that the M41 was too big to be a good recon tank in comparison to the M24 Chaffee, but it was a decent size for an infantry support tank.
The M551 Sheridan is 2.8m wide and 6.3m long. Carrying Sheridans 2x2 would require a cargo bay at least 5.6m wide and 12.6m long, and probably closer to 6m wide and 13m long, cargo weight of 136klbs.
Tanks 2x2 would make for a chonky looking cargo lifter. very fat fuselage diameter but short length.
For the AW.681, I could easily see it flying on straight-through Pegasus engines if the VTOL requirements didn't happen. 28klbs of thrust each beats the heck out of Medways making 13.7klbs. Or, keep the split fan nozzles and drop the hot nozzles so the core blows straight back, use a simple diverter if you need vertical thrust.
