I've read that Dr. Upton and the Pi foundation had planned to do a 10" one a few years ago but for whatever reason it was abandoned. I asked Dr. Upton about this during his AMA on Tom's Hardware a few weeks ago and while he didn't confirm much (not that I expected him to) he did elude to a possible refresh soonish....
Q: I'm a huge fan of the official Raspberry Pi 7" touchscreen. Are there any plans to release a larger 10" touchscreen down the road? Any possibility of an updated 7" touchscreen that will position the Pi in reverse (arranged so the power cable does not plug in on top)? Will there be an updated case for the 7" touchscreen for the Pi 4?
A: An updated touchscreen is drifting towards the top of our to do list. Definitely hear you on plug positioning. We don't do a touchscreen case at the moment, but I'm aware of at least one third party who is investigating a Pi 4 + touchscreen case.
Here's to hoping a 10" version will be announced. I'm planning to mount a few Pi's in-wall with the POE hat and touchscreen as home "control" panels/picture frames. I could do it now but I suppose I'll hold off a few more months before cutting holes to see if anything is announced.