mev-boost provides the foundation for a competitive market of block builders, each trying to provide the most profitable block to validators. Naturally, some searchers should want to become builders themselves. We expect there to be multiple relays in the future with varying requirements on who can submit blocks to them and how those blocks can be submitted. We are currently working on the rules for how the Flashbots Relay for mev-boost will accept blocks from builders.
If you are interested in becoming a builder or just want to learn more, check out this issue on mev-boost.