At some point old pubkey coins might be easily hackable.
Whelp, that certainly puts my mind at rest

It is a safe assumption that cryptography can be broken (at some future X point) so you just have an arms race where you upgrade your cryptography and move your coins to better cryptographic schemes when vulnerabilities appear - or ever earlier. In any case, preferably, before you get cracked

It's no different for governments or banks really. You just have to be ahead of the game.
The speed of quantum computer development took the NSA and everyone else by surprise. Nobody thought Bitcoin's cryptography could be broken when Bitcoin was invented. The whole internet depends on that same type of cryptography, and quantum computers could break it.
There's a scramble to develop new quantum computer resistant cryptography now. Bitcoin will have to swap to it sooner or later, at which point a decision will need making about Satoshi's coins if he doesn't claim them by then.