Look at the wording of the law (or claimed violation). They do not want to register any vehicle tgat does not meet the FMVSD. It isn’t just kei cars that don’t meet the FMVSS. Neither does any of the other “forbidden fruit” cars that are now at least 25 years old and being imported. Integrales, R32 Skylines, etc. do not meet FMVSS.
I left Illinois for Texas. Illinois is a backwards state where the people willfully have voted themselves the same people over and over and wonder why it gets worse and worse. In Texas I can drive my car year round thanks to usually good weather. I do worry about the people moving over who may not have learned why their states are all kinds of messed up.