Miners do not endorse any soft forks with signaling. Neither this BIP nor BIP 8/9 signaling is meant for endorsements.
Users are signaling support as mentioned in the BIP draft. All transactions will be mined sooner or later if there is at least one pool which can include it in the block.
Ocean pool (default template) already excludes transactions with nLockTime 21. This BIP does not create incentives for censorship. All transactions will eventually get mined except if all miners decide to exclude it. In case, all miners ignore a transaction, users can use a normal nLockTime to replace the original transaction or increase fees.