FCC requires electronic devices to both accept and not emit interference as a part of a certification. That may be a hurdle for the development process.
I meant to say 'a serial ICE/electric'. An example would be GM eAssist.
ecomodder.com/forum/.../controller-mods-build-e-assist-altermotor-35003. This is driven off the crankshaft with a serpentine belt, rather than after the transmission. Presumably that would have a planetary gear or clutch or something.
The eAssist uses a fairly modest battery, compared to a full EV, at 115V or so.