Let's be specific here. Mining pools sell their expected block space, and they have always been able to decide what transactions they want to include in their block templates.

This has not really been an issue, since fees have generally been a smaller portion of the block reward than the subsidy, other than a few notable exceptions. But as miners begin to rely more heavily on fee revenue, they are likely to put a premium on prearranged, and even prepaid, fee income.

Right now the fee market is almost entirely handled via our nodes' mempools and is only interested in the fee rate to make it into the next several blocks, but that very well may change, and particularly institutions will be interested in locking in guaranteed fee rates for months into the future, if mining pools are willing to offer it to them.