I was just thinking about the idea of having three alphabets: Latin, Greek and Cyrillic... 0x00 - 0x7F for Latin, 0xC1 - 0xD9 for Greek uppercase, 0xE0 - 0xFF for Cyrillic uppercase.

Both Greek and Cyrillic would be uppercase only and would be goofy to enter:
- Select greek keyboard layout and type with capslock on
- Select russian keyboard layout and type in all lowercase (which would look like caps)

...of course I have no use for this and I'd be surprised if anyone else wanted something like that, but it seems possible.