If it’s three years away that means state-level actor(s) has it now.

I wonder what a quantum backdoor would look like.

My sense is that if a threat actor were able to build a quantum computer to the scale of being able to compromise public-key primitives based on the difficulty of integer factorization and discrete logarithms under the key sizes used in practice today, one of the highest-valued targets will be Bitcoin.

There is no billion-dollar annual market for quantum compute usage in private industry. Yet these companies are getting billions, and it ain't all grants, stocks, bonds, and notes. Ain't rocket science.

On what do you base that assumption?