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.

The aluminium weight is the same material as the case, but it is just coloured in a copper look?

I picked up the Cipulot R1 RF 87u PCB from CannonKeys. It was probably not necessary, but gaining QMK support was a big plus for me. That turns this board from a fun weekend board to a productive daily driver with Space-FN etc.

At this point the only thing left from the original board will be the plate.... which I might as well have cerakoted because we're pulling out all the stops here, I guess.

I mean qmk is big for tkls at least, I really don't like the standard layout so it's big that I can reprogram it. Might grab a replacement pcb/adapter so I can reprogram my layers better for my hhkb, and that is a layout that I really like.

what is the benefit of using a steel plate... is it a sound thing? i thought we were past that

We chose to utilize a stainless steel plate because it contributes to a unique sound profile and also provides a more solid and satisfying typing experience.