We could consider deprecating passing `false` in 2.99, but we can't consider deprecating passing `true` in 2.99.  The point of 2.99 is so users can get to a warning-free state, and then upgrade to 3.0, trusting things will work.  If a user relies on this feature (which many do, I think), then we don't want to give them a warning about setting this to `true`; if they stop setting it to `true` in 2.99, it'll break stuff (as they are relying on this behavior)...so they would have to just ignore the warning.  But we are telling them "upgrade to 2.99, make changes to get warning-free, then upgrade to 3.0".  If we deprecate this in 2.99, users can't get to a warning-free state before upgrading to 3.0 and that will cause confusion.  2.99 should only contain warnings for things that should be changed before upgrading to 3.0, and this isn't one of them.

As for deprecating it being set to `false`: I don't see a particular point there, either.  If they have any code that relies on this not being `true` (whether by not being set at all, or being explicitly set to `false`), they will get deprecation warnings from their use of symbols via the code in `MetadataHashBuilder`.  The only way for someone to have a test suite where this is set to `false` and for them to not get any deprecation warnings is if they don't rely on it being set to `false`.

So...it seemed best to me just to deprecate it in 3.0, an leave 2.99 alone.