Future plugins allow use of old mods?

I have limited experience in C++ and understand that if I get a job developing in C++, within the next 20 years it is likely that it will be used predominantly for kernels for higher level languages to run on. I also know that the C# version and Java versions of minecraft will be sporting a plugin system tricked out to allow minecraft to be microsofts definition of "fully customizable". If they held their word and TRULY made minecraft fully customizable via plugins, could Forge create plugins that would allow mods from old versions of minecraft. While I know this may or may not be very worth while for the developers of forge. I am simply wondering if this is theoretically possible, even if it is not feasible.