I wouldn't bet on that. The problem sizes expand to fill the available hardware.
Yet the volume of space mostly taking up in the current Mac Pro is mostly by fans and ducts, and expansion cards inserted vertically, not storage, not ram, or anything else.
place expansion cards horizontally, and with fans and all else, you get a wider foot print, yet a much smaller height in the case. As stated cooling may not be heavily needed going to apple silicon in the design archectecture. Power consumption also will drop, significantly even if compared to the latest Intel & best of NVidias video cards. If apple can match on both fronts of what the competition could launch this year into middle of next year then they’ll have a winner.