A couple of ideas I've had of but not developed:
• Analogue joystick for scrolling, similar to a IBM
Scrollpoint. Emulate a high-resolution scrollwheel (Microsoft's convention of "resolution magnifier" in the HID protocol), but look also at tweaking the input incorporating "negative inertia" like IBM Trackpoint.
I've seen keyboards with multiple joysticks but I dunno if one was used for scrolling.
• "Natural Keyboard"-style ergonomic keyboard, but split and with with
adjustable tenting, mating with flat parts of the keyboard without gaps. Don't just use adjustable feet but actual
hinges. A keyboard frame made of sheet metal could incorporate "invisible hinges" in the frame: a pantograph mechanism hidden below the top surface so you don't see it. Alternatively, curved sliding surfaces (sectors of a circle with origo at the gap in the surface) and a pin and/or spring could be used.
• Integrated trackpad in the top surface. Not just a separate component but integrated into the top case utilising all the available area.
I've seen buttons on the
left side of some recent Bluetooth keyboards: for on/off and pairing (Bluetooth), and I think one also had some media buttons.
The
HHKB Studio has touch-sensitive sliders on a couple of its side edges.
I remember from the forums long ago that someone was working on a 60% with Trackpoint that had the mouse buttons on the front, but apparently it never reached mass production.
Unfortunately, the USB HID protocol does not support adjustable repeat rate or motorised sliders
itself. You'd have to develop a custom driver or something.