A way to overcome compability issues on this new version and with very limited effort is if you could add an extra preference that starts something that recognizes or reads from the cpr on what version of cubase it was made on. Then it would load up the correct cubase version (where the song was made on, with al it’s original plugin settings and other settings)
It comes at very limited cost, since it is allowed within the license limits, and the only thing a user would have to do is download or use the installed earlier versions of cubase with all it’s paths to the vst’s that were installed on that earlier version. Most likely this setup would be present on such a user’s environment.
This could preserve loss of material that was made with earlier versions in some way that is very user friendly.
Ok, you can just start the older version and do the same, but the cpr’s normal boot program is rewritten towards the newest version normally when you install a newer version, with popups and disfunction presented when the cpr is loaded up.
It’s something simple maybe, but with much added value for long time users.
If this setting is already present in the program, then sorry to have posted this, but i would like to hear where that preference setting is located in the program now. 
FWIW
kind regards,
R.