I think you underestimate how big the number of 2^128 ECDSA operations are. It is 20 orders of magnitude bigger than the puzzle that was just solved (that took 2 years). There is no way we scale our compute that much in 70 years unless we start building Dyson spheres.
To answer your question that change in bitcoin can happen at any point in time with a protocol update. It would probably won’t even require a hard fork, a soft fork would suffice.
> no way we scale our compute that much in 70 years
Huh? Ask someone in 1950 if we would ever achieve petaflops on a desktop-sized PC. Yet here we are with H100's. About 10 decimal orders of magnitude faster than the state of the art in 1950.
Quantum computing will also happen, and I think 70 years is more than a realistic time frame.
To answer your question that change in bitcoin can happen at any point in time with a protocol update. It would probably won’t even require a hard fork, a soft fork would suffice.