before Bitcoin, I believe there are lots of low security that will be cracked first giving a hint that there is a need of an upgrade of security for Bitcoin hence the possibility of your speculation or prediction might not happen.
or look at this way: anyone producing a sufficiently powerful quantum computer probably has big interest from the "local military" so to speak.
because that kind of equipment has military implications; whichever political faction who obtained such a tool first could use it to:
- outright attack enemies
- blackmail them instead
it would be a world changing event, if it came out of a clear blue sky (i.e. unexpectedly). One could pwn everything and everyone with such tech, a whole new era would begin rather abruptly
guess what though? everyone to which any of this is relevant already knows, and is preparing accordingly. Bitcoin devs are only one out of many who are aware, and they don't yet have any (known) military connections