The question now is, define "very old", and at what threshold or age do "old coins" expire and are no longer redeemable or spendable?

Most fiat bank accounts of the world have some sort of 10 year time limit on "dormant" accounts, but 10 years might be too short. Perhaps there could be some sort of fork (soft or hard) where "very old" unspent UTXOs are expired after a certain future time, like 10 years from now, but only if they are still stuck in legacy addresses. I think any coins in newer segwit addresses (or future taproot addresses) should never expire as some people may be holding on to them for the next several decades.

It is good practice for wallets to move coins every year or two but that's besides the point.