Public-inbox repositories (the data layer behind
lore.kernel.org) is not just an archival medium, but also an efficient git-based message distribution platform. You can clone all data behind
lore.kernel.org *and* keep it continuously updated.
For example,
https://lore.kernel.org/b4-sent/ contains submitted patches there never touched SMTP but were submitted via b4's web submission endpoint. A tool like "lei" is able to retrieve these messages and deliver them to reviewers without any of it touching the much-hated SMTP protocol. Yes, "lei" is a backend tool that is not very end-user-friendly -- the goal is to offer it as a service delivering query-based results into its own public-inbox feed that is available via POP, IMAP, or any other message retrieval protocol, plus fed into patchwork.
Evolutionary change is how we'll improve the situation, not by introducing centralized, single-point-of-failure, outright proprietary or "open-core" tools.