Maybe even a new Pro Display XDR.
After a years-long drought in the Apple displays department, this kind of revelation gets the imagination going.
So, speculate we shall!

B&H Photo video
“professional photographerandphotography bloggerBikram Pachhai told Lifewire via email.
You don’t even have to write new software for it.
Just adapt the existing iPhone and iPad stuff.

Nana Dua / Unsplash
But what else could this enable?
Display Everything
How about building in an Apple TV?
Speaking of which, how about adding AirPlay?

Mohamed Kerroudj / Unsplash
Who wouldn’t love to unlock their Mac just by sitting down at their desk?
Touch Screens
Finally, how about touch screens?
Apple makes amazing multitouch displays for the iPhone and iPad.
Why not make a touch-sensitive display?
Add in Apple Pencil support, and Apple would probably sell a few of them.