Quick ideas.
Wait until all pending soundness fixes are ready to go and turn them on together to limit the repeating pain.
Whitelist these exact crates, leaving them as warnings, turning errors on everywhere else, to give the broken crates more time.
Submit patches upstream right now so that when the error hits stable in 6-12 weeks or whatever they will hopefully be redeployed. Although this is a lot of breakage, we could probably get a big chunk of the patches done in a day. I’d be happy to help with this.