Re the "Manhattan project in 1944" argument - I am very cautious about the "modulo engineering scaling" carve-out -- unlike the uranium manufacturing pipeline of World War 2, that involved massively scaling up a known process, on the face of it there's no uncontroversial process/architecture to scale up in this case.

On the face of it, even relatively "point-target" goals of this kind could take many decades if at all; GaN for blue diodes come in mind as an example of a field that was stuck for a generation -- until it wasn't.