Dan, respectfully, please don't terminate the previous version, there will be users who stay with older versions, that's just the way it is, probably always will be. Just a note about the term 'deprecate', when you say something is deprecated, you aren't saying it's terminated, you are saying it's still available and completely usable, but that there's another option that is now preferred over it. For example, Microsoft would say that Windows 7 is deprecated in favor of Windows 10. Many users would disagree, and continue using it.
I would prefer that auto update be turned off for the previous version, so that the Recycle Bin still works for all users, no matter what version they decide to use.
Better way is a completely separate plg file for the new version. With the appropriate template settings, CA will only display the one that works on the user's system, and in the case of a later upgrade, FCP will catch if the incorrect version is installed