Here's a list of firmware requests for the X-H2 / X-H2s I've either had myself or collected from videos/reviews. Feel free to add more or disagree/agree in comments!
Control
The ability to put ISO on a dial.
Switch to Nikon ISO adjustment style (press + hold ISO button and use wheel, let go of ISO button and it selects, instead of tap). I came from Canon many years ago, but Nikon's system is much faster!
Disable expanded ISO (helps make ISO adjustment faster)
This may not be something everyone agrees with, but I'd like them to remove auto-ISO from the ISO adjustment menu, and put it in its own menu. Why? Because I want 125 to be the hard stop at the bottom when I'm quickly trying to re-adjust ISO with the wheel. Alternatively, give me a way to assign switching to a specific ISO setting to a button with one press. Basically, ISO adjustment is too slow and fiddly!
A menu option to toggle the camera between 1/3rd stop adjustments and 1/2 stop adjustments for shutter/aperture/ISO. 1/2 stop makes doing manual adjustments much faster.
The ability to assign a button to turn on and off any interface element in the EVF. The one I want in particular is the grid-- I would love to be able to quickly turn this on and off as needed.
Pixel-shift
In-camera combination of pixel-shift, or at bare minimum some way for the camera to mark that the cameras are a pixel shift group so they don't get lost before I load them into the app on my computer.
Autofocus
A better system for switching between AF subject detection for face/various kinds of animals. Currently I need two buttons (face and subject) and I still need to go into the menus to switch between subject type!
It does seem as though autofocus needs a little tuning. The box in continuous tracking mode tracks things well, but if you try and shoot at the same time it "misses" some of the shots. This feels like asking for the moon, given how much AF as improved, except that Canon/Nikon/Sony/OM does this pretty much bulletproof now. Fuji is close, maybe they can get to 100% in an update...
Thats all! Honestly for me the "control" options are most important. I picked the X-H2 for the viewfinder, but If I'm going to give up manual shutter/ISO dials, the command dial system has to be perfect. Love it so far but there's a lot they could improve with little changes.