Adam Majer [off-list ref] writes:

Is sha256 still considered experimental or can it be assumed to be stable?

I do not think we would officially label SHA-256 support as "stable"
until we have good interoperability with SHA-1 repositories, but the
expectation is that we will make reasonable effort to keep migration
path for the current SHA-256 repositories, even if it turns out that
its on-disk format need to be updated, to keep the end-user data safe.

So while "no-longer-experimental" patch is probably a bit premature,
the warning in flashing red letters to caution against any use other
than testing may want to be toned down.

Thanks.