Can we decouple tx fee from the txs themselves?
Bitcoin mining is business. It incurs significant hardware and energy costs. So it's absolutely understandable and legitimate that the commercial miners choose those transactions that give the biggest overall fee. And a 10-Satoshi transaction occupies the same space in the block as a 100-Bitcoin one. It's a bit like in real life: some countries in the Euro region don't circulate 1- or 2-cent coins because their production costs more than their nominal value. And everybody there accepts that a change of 1 or 2 cents is lost.

Your suggestion is implementable within the current bitcoin consensus if you can convince a significant portion of the miners to follow that scheme. Every miner is free to implement his own priority scheme for transactions, not necessarily based only on transaction-internal data.

But I doubt that you'll be able to convince enough miners and users to switch to that scheme. Miners will lose fees, and users will have to pay in advance to get a token that's only accepted by a (small?) portion of the miners.

If you want to help with low-volume transactions, start your own miner with a priority scheme that prefers low-volume transactions. You'll lose money running your mining hardware, but some users will benefit.