I like weird ideas, and I like this one.
The 2 big challenges that kind of made me give up on my electric motorbike were:
1 - No matter what you're going to have a very short range, can't really enjoy a trip anywhere, and
2 - Even for the range you have, there's nowhere good to put the batteries.
But as Remy points out, floor of the sidecar is perfect. If you want it to be electric, just drive around with the empty sidecar EV. If you run out of range, no problem start up the ordinary gas powered motorbike. If you want to go somewhere without the EV, ditch the sidecar at home.
Gives up the sporty part of a motorbike, and, I guess at that point you're just driving a really terrible and uncomfotable convertible with no cargo space but... hmm... I did decide to save my batteries for an EV car instead.