If you recall reading my old "wish lists" you will see that the Pi4B meets or exceeds all of them. That said, there is the story of the Walter Reuther (head of the United Auto Workers--UAW--union) was asked what the UAW wanted. He replied, "More."
Personally...a very mild "nice to have" would be to get the USB ports up to full speed. Not important to do so, 4Gb is close enough to 5Gb, as it's fast enough to fully support SATA-II (3Gb/s) speeds, but even 5Gb won't fully handle SATA-III (6Gb/s).
Since the RPT saw fit to go to dual HDMI outputs with 4K capability, a logical extension would be to support 2 x 4K60 or--possibly--a higher refresh on a single 4K output. Long term goal would (5 - 8 years?) probably be to push toward 8K output as that is becoming a thing. Again, not something *I* need as the highest resolution display I have is 1920x1200 and every Pi I have handles that quite nicely. Though if the budget supports it, it'd be fun to get at least one of the Packed Pixel 15" 4K panels for a portable (or, at least, easily transportable) system.
And speaking of video... As I understand it, the DSI output is close to its limits with the 7" 800x480 display. Finding a way to increase the DSI bandwidth in the future so the Pi could support (and the RPF could produce) a 10" HD resolution display would be really nice. I have at least two systems I would upgrade if that path were available.
In general, I would happily support running cooler at this point over running faster. I can't imagine anyone turning down an option for even more RAM, but I don't see any actual need for it in anything I'm doing or plan to do.
And to make the point again....I find the Pi4B meets or exceeds *all* of the current hardware requirements for my projects and I don't see that changing in the foreseeable future. I do want boot-from-USB, but that is coming and all I have to do is upgrade to it when it arrives. The Pi4B is a really slick machine and I love mine (4 so far) and plan to get more (at least 5 more, as funds permit).