All,
There is a new Libraries Proposal process, inspired by the GHC Proposals process.
Core Library APIs are critical. It's easy for a sensible proposal to languish or simply get dropped on the floor; and (in the other direction) a bit too easy for a proposal to make it into the core libraries without receiving the scrutiny it deserves. Most of the proposals that have been made on this mailing list, become lost to the archives. It's not easy for anyone to answer the question "what decisions has the CLC made recently?" without trawling a huge email archive.
Of course, this is mostly for breaking changes or "big" introductions; we don't need a full proposal over something tiny, e.g. "a module from vector is missing a fold". That would be more appropriate on vector's issue tracker, and left to the maintainers to deal with.