Is that actually confirmed policy or just guesswork? The closest thing in the migration plan seems to be "The focus of our development will be on the swift-foundation package", which doesn't sound to me like no bugfixes for SCF, but maybe I'm missing something.
Fwiw, there were a number of PRs merged in the last week, although those are to the package branch and seem to be part of the transition to the new Foundation package. There have also been a number of PRs adding Sendable to some types, most of which were merged.
@Tony_Parker is adding Sendable to NSLock in SCF something that could be accepted at this point in time? I know the long term plan is to address discrepancies between Darwin and other platforms by unifying the implementation, but this particular case seems extra unfortunate due to the urgency implied by the warning.