Is there any difference in practice if you take away 5% of coins from each address that has unmoved coins from 2010, or if you make them pay a 5% fee to move them? No.
In general, tail supply, where 21 million coins limit is broken, is a sneaky way of getting coins from each user. Because then, users preserve the same amounts as before, but they can lose value over time, because of newly produced coins.
Yes, I am against any such proposal. It is just reinventing inflation and giving it new names.
However, when tail supply is introduced without touching 21 million coins limit, then users can really see, what it is about: it is equivalent to taking proportional amount from each and every UTXO, and redirecting that to the miners.
Which means, that if someone will introduce "tail supply fees", which will always be allocated into future block rewards, then it will work in exactly the same way, as tail supply would. It is only a matter of picking the right numbers, to preserve all proportions, that someone wants to achieve.
I am less against such a proposal, but as long as it is fair. It is even ridiculous to propose to punish me for my strong belief in Bitcoin. Proportional amount from every UTXO makes much more sense than anything related to coin age.
It's an interesting phenomenon that will play out through the years but so far Bitcoin's strategy of doing nothing has worked best. If anyone feels as if there's a need for mining to continue, they're more than free to contribute their cash towards starting an annuity. The legal landscape for that already existed hundreds of years and it's easy to do.
As I said, there is no problem right now. There is only speculation that it may become a problem, but nobody really knows. If they pretend that they do, they are just another snake oil salesman. While we observe what happens, we can use the time to discuss proposals and not rush into anything radical.