How many versions between Cubase and projects can it be before you cant open them anymore
The CPR file type is here since Cubase SX 1 (released 2002). So you can open 20 years old projects. Cubase SX 3 was the last one, where you can also opened the older Cubase file format ALL, ARR.
Of course, such an old plug-ins will most probably not exist anymore, so you get the Missing plug-in message. But you will get your project.
Lets say you can open Cubase Pro 11 in Windows 10 but how many Windows versions after Windows 10 can it be before you cant open Cubase Pro 11 in Windows at all and therefore need to upgrade Cubase or need to buy a brand new Cubase
Oh, that is really a question for Microsoft. You should head over there and ask them when they intend to release a new OS with a significantly changed architecture.
At least one.
I wonder if your question is tongue-in-cheek… but I’ll presume it’s not.
The answer to that question is given by Steinberg every time there’s a significant OS update with changes that might break Cubase.
So your best bet is to travel to that future date you are thinking about, see if your system still works and check it out.(don’t forget to bring your computer and keyboard with you!)