If I understand correctly, the idea is to allocate a pre-confirmed portion of block space for proposers to include transactions.
Correct.
Proposers can receive open market payments through MEV-boost relays, ensuring fairness by prioritizing these transactions top-of-block (TOB).
This depends. If you use the mustBeginWith field in the payload, and use a mergingPolicy which privileges preconfs over traditional MEV-boost, this may not be true anymore, as preconfs would get TOB. It really depends on how one runs the system but yes, I agree with you that what you wrote is probably the most obvious and wisest way to run it, lol.
From a proposer’s standpoint, they benefit from participating in a dual market scheme while maintaining the flexibility to optimize their proposer payments.
This enables optionality to the existing block space market without requiring any breaking changes.
Yes. This is the main point of the idea. Also, this results in very little changes to be implemented from the proposer’s POV. Ironically, Vitalik is giving a talk today called ‘Don’t overload the proposer’, I guess at least my timing was right 