I don’t have a source handy, but eventually block production will centralize and the protocol will allow a “block proposer” role which will require lower resources. The proposer will be able to force a producer to include specific transactions and if they aren’t included, the producer will be punished (via their stake being slashed).

If a centralized entity is told to include transactions by a proposer and they refuse for any reason, they will eventually lose their stake and fall out of the producer role.