Nic Carter has an idea toward that end, I'm not sure it he ever wrote it up. Basically tax unused utxos after some time to keep the mining rewards higher for longer. The complexity and push against ta...
Requiring a percentage of old coins to be spent as fee will not work. People who are able to build a quantum computer can also spend a few more bucks to buy miners and mine the block containing the transaction themselves, without broadcasting it before.