Of course, everything below is from a bit of an outside opinion as I've only been in the stands once as a foreign fan.
The basic concept of safe standing is good, generally agree with
@BilbaoCherry 's point that in the long term it'll likely be a plus for atmosphere and possibly bringing in younger fans. However, as others have pointed out, I have issue with them doing it in the middle of the season with such a rapid turnaround, this should be done over the summer with more time to make sure everyone affected has time to be properly notified (not just one email), make an informed decision, and reallocations be made. As it is, I can definitely see some people missing the email, being frustrated by showing up for a game and suddenly being in a safe standing area when they don't want to or can't stand throughout the game, and the club having to deal with figuring out relocations well beyond the current period they've appointed for it (and if they refuse relocations beyond it, that'll be a travesty, but let's hope we don't run into that).