E-bikes meeting the federal requirements are not classified as motorized vehicles by the RMV in MA. Please see the bottom of this form:
www.massrmv.com/rmv/forms/21897.pdf
"Motorized vehicle" is a term of law, and this requirement for a drivers license would apparently not apply. Some ebikes might exceed these requirements, though. In this case, the bike would also need to be registered as a moped.
This is, of course, a completely separate issue from federal preemption.