1 extra (literally) odd bit would require a lot of changes...

What if instead of using single bytes, we used "doublebytes"?

8-bit software continues to work, while new 16-bit "doublebyte" software gets 256x the value capacity, instead of a meager 2x.

Nobody will ever need more byte space than that!

Without requiring any changes to CPU/GPU, RAM, SSD, Ethernet, WiFi ...

Magic. :)