Let's assume for a moment they want to go ahead and disable this accidentally enabled feature, OK, but they should have changed it such that - On existing installs: You could mount existing volumes, but not create new ones - Start showing a warning to users asking them to migrate - If they are desperate, on new installs, you could potentially disable mounting existing volumes or at least and a stern warning. (The downside is for example, if your NAS died, you got a new one, migrated the drives, you can't access them again. So this is a hit and miss idea, depending on how keen they are to push disabling the feature)
The good and bad news is that in all liklihood they didn't intentionally brick existing users but instead some braindead engineer went "oh that's not supposed to be enabled it, let's disable it" and didn't think about or realise how it would affect existing users until it was rolled out. Good because less malice, bad because they should ideally have smarter engineers reviewing such things.