I would agree, but that seems like a lot of work, unless you can reverse engineer their BMS, have a 3d printer to build a new housing, and just have a lot of time on your hands.
Seems like just buying 1 or even 2 battery extenders, from specialized, or even go aftermarket if you really want.
I would like to see offerings for more modular battery setups in our bikes that had the ability to utilize a half sized battery pack, but easily joining them together for a full sized battery unit. Also, there is a lot of space that is not utilized in our frame, that could allow for a few cells placed in different locations in the frame or even other components like BMS, in our chain stay, seat, top tube, steer tube, etc.
I think this would allow for more unique, possibly slimmer frame profiles, but in current profile provide options for traveling with ebikes, increasing range for long bike-packing adventures, possibly not utilize water bottle holder for current range extenders, etc. I mean think of what a carbon frame could look like if they weren't stuck using the same 2.5x2.5x12-16 rectangle battery packs.