[wmf]

OK, what you're saying is that after the block reward ends, fees will equal miner revenue and miners will mine harder until equilibrium where their costs equal their revenue. That's correct but it's important to understand that the causality flows from fees to miner costs, not vice versa. Miners cannot force fees up or down.

[leijurv]

Well it's a continuous process: today the fees make up maybe three percent of revenue, but that fluctuates as transaction space demand changes, and as the coinbase halves every few years.

But your point is good - miners are not really in a traditional supply/demand relationship with transactors, because block space is perfectly inelastic. There will be 7 slots per second (amortized), no matter what. Although... a petulant miner could artificially restrict this supply, by perhaps declaring that they'll never mine a transaction that pays less than X fee. This would only apply to the blocks that they mine, but the effect on overall supply could be nontrivial?