Why not taking a PinePhone approach of exchangeable back covers offering different add-ons?
PINEPHONE & PINEPHONE PRO PINEDIO LORA ADD-ON CASE - PINE STORE (pine64.com)
PINEPHONE & PINEPHONE PRO FINGERPRINT READER ADD-ON CASE - PINE STORE (pine64.com)
PINEPHONE & PINEPHONE PRO KEYBOARD - PINE STORE (pine64.com)
I could definitely see the sense in stuff like extra battery pack add-on. Yes, the L5 would get crazy thick, but it would be a choice of the user.
And under the same logic there could be a FeliCa add-on case.