You can leak all three internal temporary registers on the V20, which would be extremely fun to try to emulate without a microcode-based emulator.
The eventual idea is to have microcode-based cores for 8088,8086,V20,V30, and 80286 in MartyPC.
I'm not sure if a microcode-based 386 is practical in software. I think MartyPC might just stay 16-bit forever.