We all wanted this. SIGH
Having worked in the Apple Stores as a Technician, this would not work right now.
#1: a screen that takes up the entire device, in this case, would lead to a much larger casing in back. This would defeat the purpose of what Apple has done with the iMac for some time now: having a thinner over all computer
#2: Without the "chin", you lose access to space for the system board, the larger speakers that are befitting the iMac, and the cooling fans. The fans are the most important part in this case due to heat dissipation for both the logic board and the display. A display this large would generate a pretty significant amount of heat within the casing. Especially when you consider that the logic board would also have a better integrated graphics chip than the MacBook Pros currently.
MacOS is still a much more powerful OS than iPadOS is. The inevitable direction would be to create an iPad that could run MacOS or a unified OS, but it does still require more power overall. With the requirements for, again, heat dissipation, higher graphics processing, etc., this design would not, currently, work as an iMac.
Now...as an external display to replace the old Thunderbolt displays... 🤔