Right - but when speculating consider the actual timelines and realistic events. I think it's quite clear there would have never been enough Mosquitoes to supplement or replace the B-17 and even if we used that "speculative scenario" the Mosquito "would have" had so start rolling down US production lines a least a year before the war started (for the US).
Well like I said, I think there are three discussions to be had:
1) Could this aircraft get the job done technically. To me this is the most interesting part because were the discussion to survive long enough to really get into the weeds technically, I would certainly learn about the operational histories, offensive tactics and defensive countermeasures which were actually used in the war.
2) Could they produce enough to make this aircraft into a Strategic weapon? Was there enough industrial capacity, technical know-how, and time to get this ball rolling? Though not quite as engaging as operational details, this is also interesting to me because how such programmes were implemented is another area I can learn more about how things really worked. I don't think, however, that it requires a total cancellation of one programme in 1940 and it's replacement by another. I can see one type getting phased out as a newer type takes over. They didn't even know the capabilities of the Mosquito really until 1942. Much as P-38s gradually replaced other US fighter types in the Pacific, or P-51s in NW Europe.
3) Could they talk the "powers that be" into making this shift? This one is not as interesting to me necessarily, simply because it's more of a matter of individual personalities, politics and influence. Though here too something could be learned. I don't claim that this part of it could have actually been solved though.
To me 1 & 2 are worth thinking about and exploring as a thought experiment. Maybe next time around, if we understand better how those two parts could work, we can better address #3. Regardless, I think it's a useful way to learn more about the air war. To me, this is the actual reason to indulge in 'speculative scenarios' of this type, to see if better decisions could have been made - if they could have worked. Dealing with the political or doctrinal side of it is another ball of wax.
And IMO, if you hate 'speculative scenarios' on principle, because 'that didn't happen', maybe you should ban such threads in the future? I didn't start this one (or the Korean war one).