4-bit architectures

[LRGH]

This is a question for cpu_rec users. Please react by commenting on this issue.

There is no reason that cpu_rec could not be extended for 4-bit architectures. It may need a few tricks, but is it useful for the reverse-engineering community?

Some examples are the HP Saturn in old pocket calculators, or some Toshiba microcontrollers in more recent pocket calculators.
One could also want to add microcontrollers such as MARC4.
Do you have examples of binaries that probably correspond to a 4-bit architecture and for which cpu_rec might be useful?
And... do you have a relevant corpus on which cpu_rec could be trained?