The problem I see with your plan is running pictrs during migration - you will still get thumbnails generated during that time. All this will lead to split brain. Not too big of a deal as you simply won’t have thumbnails for recent sites, but, technically speaking, you will still have data loss in terms of imaging. Might as well avoid the overhead of making a copy of the db.

Yep but I was thinking that losing some thumbnails was better than having image delivery completely off for hours.....