I am kind of confused by this "What will happen if such a computer ever exists is slowly attempts to mine the most static of these coins, probably the old coinbases, will occur."

But my understanding is that (in theory) these attacks won't take a lot of time and are undetectable unless the coins are moved. This means someone could gather a bunch of private keys for lost BTC over time without moving them and then move them all at one (probably amounting millions of BTC).