Faster CPU and GPU obviously. The second HDMI port on the Pi 4 could not do 4k60, and desktop 4k performance on the pi was abysmal.
One unique thing I would like to see them do is add a higher cost version with a faster CPU/GPU over the base model in order to cater to those of us that use the pi for things like NAS controllers and lightweight database or development servers. Specifically, some people use the regular pi for non demanding tasks like digital signs. Others have a desire for a small form factor board that can do the tasks I mentioned above and more. They should definitely consider creating a high end segment.
A thunderbolt port or USB4 would be nice, though it will never happen. Someone above mentioned m.2 support, but that would require changes to the board design. I have a case that adds that anyway.
Oh, a 16gb option and good availability would be nice. 🤣