I am very cautious about this approach. Simply put, it seems to reduce the permissionless nature of the system as a whole. The mechanics of an honest competitor replacement seems fairly tricky/abstract (with fair delays) and should be studied more thoroughly. Additionally, it could present an entirely new dimension to selective front-running and adds significant friction to players who want to be sure they will not be censored or conveniently delayed (arbitrage, etc.). I tend to like the idea of having an incentive system on refreshing witness data in the network, as an alternative, with a mempool sharing all transactions. If I am dealing with sensitive transactions under certain circumstances where I should not be paying additional premiums to prevent intentional delays from centralized aggregators, being able to run my own nodes and just broadcast to a mempool seems much more preferable.