With ePBS being SFI'd for Glamsterdam, we will likely see some major updates to the builder-api.

TLDR; ePBS introduces a mechanism to stake a builder in-protocol and have a mechanism to trustlessly pay a proposer for including an execution payload.
Certain relays/builders might not choose to become a staked builder and might want to still run off-protocol like how it is today. In such scenarios, it would be good for us to understand how the builder-api would change and design it accordingly so that there is a standard for implementing it.