I am sure Sony can stitch two Sony CMOS 33x44mm 50mp sensors together and make it work.
For what people would want in a 6x7 "artistic" medium format camera (as opposed to a scientific or technical tool) it does _not_ work to glue multiple sensors together side by side. This "butting" is already done for other purposes, like X-rays, machine vision, telescopes and aerial photography, but there are visible join lines many pixels wide, which would ruin "artistic" photography.
The "stitching" already used to make bigger sensors like 36x24mm and 44x33mm is done during etching of the sensors onto the wafer, and is a high-cost, low-yield process, with "cost per usable sensor" rising rapidly as sensor size go up and so more pieces much be stitched.