I always wondered why they couldn't put a biogon style lens in the TLR. It would require a different design for the viewing lens and taking lens (there's still a mirror for the viewing lens, albeit it needs less clearance than the swing of an SLR) but it would be so cool and they could have relatively easily made an ultrawide for the system.
My personal theory on why there is no floating element adjuster for the TLR is because it was prohibitively difficult to design into the dual lens design because the barrel can't be larger than 58mm or whatever or else it will hit the viewing lens's barrel. It may also have to do with the target audience of the camera which may have been less concerned with corner sharpness than the RB67's target audience. What these audiences were, I am not quite sure.