It seems that the new Canon Cinema EOS C700 camera has been designed from the outset with additional sensors in mind. This may include Full Height S35 18×24 mm, Full Frame 24×36, VistaVision, and possibly other formats. It will most likely depend on feedback from users, rental houses, cinematographers and camera crews.
This is not an official announcement from Canon. But I don’t think I misunderstood when the concept was explained in meetings at IBC. Future upgrades to larger sensors may require different circuit boards, but this has been factored into the camera design as well. The idea is to have one camera body that can be updated and expanded–without having to scrap the housing, chassis and major assemblies.