A solution to the inflation under zero / lost coins in the distant future is just to add some rule in the consensus where, if coins are not moved every 20 or 200 years (full nodes consensus is implied, maybe it should be configurable by the node operators) miners can just take a part of them (maybe starting with the smaller balances).
Maybe, if the mean fee is x, everything lower than x/2 can be taken after 20 years it stops moving.
It would be like:
if there are $ 0.02 left there for a century, can we take them?
Nodes: Yes. not a problem.
If there are $ 200 left there for one year can we take them?
Nodes: No!!!
Good idea. But the simpler solution is to keep producing new coins at a moderate rate. I think some altcoins do this already.
Well, I do not think so, that kind of "cleaning or recycling" would not be well seen by most of users, that is too arbitrary, besides it's too early to worry about that and nobody guarantees that it survives so many years, at that time the nodes would have to be renewed several times at least, and the blockchain could be immensely big, whether they choose hardfork, softfork or total replacement.