You may be 'putting the cart before the horse'...the B-29 was designed as an eventual replacement for both the B-17 and B-24, using lessons learned from operational use of those aircraft.
The first B-29 didn't fly until late 1942 and the decision was taken to initially use this type against Japan due to the very long range flights involved. Type development, or ironing out the bugs, always takes a lot of time ( as happened with the Me 262 ) so in war it's often a case of making the best of what you've got.
It's an interesting 'what if?' though - if things had happened quicker, picture swarms of rocket-equipped Me 262s hacking into massed formations of Superforts at high altitude...
