The terrific looking B-36J, the plane with 6 turning and 4 burning engines, was it possible to upgrade? Maybe making it capable of inflight refueling, modified turboprop engines like the ones on the C-133 and maybe new jet engines.?
The YB-60 is close to what you're talking about. This gave the B-36 eight jet engines and swept wings to compete with the B-52. Although it had a bigger payload, it was 100mph slower and suffered handling problems, so lost to the B-52.
The vulnerability of the B-29's to USSR and later North Korean MiG's in the Korean War means piston engined planes were on the way out. The '36's max speed was almost the same as the '52's cruise speed.