What are they odds they wouldn't quietly slip these changes with a minor update under a non-descript "Security improvements" after everyone calms down and buys a new shiny iPhone 13?
Doesn't matter which version of iPhone one has, as applicable to the next version of "iOS". So assume you mean after people update to the next version of iOS. In which case they can disable iCloud Photos if they are concerned. Though they will need to also make sure not to use Google Photos or use Facebook since I assume you are aware both of them already do this scanning server side so in a much less privacy minded way.