This is already done — Swift 5.10 is already that last release series where bootstrapping is fully supported. To the best of my knowledge, Swift 6 has never supported bootstrapping, because the compiler pipeline is focused on the Swift-based driver. This isn't something that could be reasonably "temporarily" undone for a release of Swift 6.
I think at this stage, it would make sense to rip out mentions of bootstrapping from the build system, to make this more obviously official (and document this more explicitly to make it clear what the expected process should be like).