At a general level, it is clear that the Mk II offers far more flexibility in physical implementation, together with much less wiring complexity. I can immediately identify several possible configurations that would meet a variety of operating scenarios:
Full station controller: Effectively the Mk II equivalent of what I built as my Mk I implementation. This has a screen and two VFOs, with plenty of switches and encoders.Unlike the Mk I, the host PC could also be built into the cabinet, providing a complete station computing solution in a single package. Or, use could be made of an existing PC or laptop - the connection is, after all, just a single USB port.
Mini controller: A cut down version that could be perfect for travelling. Perhaps just one VFO and fewer encoders/switches. Still a display though. Same options for the host PC, although it seems more likely that one would use a laptop in this configuration. The controller could be put in a shallow box, perhaps a sloping panel, for ease of carrying.
Micro controller: Like the mini controller but without a display. The display would, instead, be shown on the host PC screen. Or perhaps not even displayed at all, as all the information you need would be shown on SSDR, which would have to be running in this configuration.
The upshot of all this is that a single set of code could be used to create a controller of any level of complexity, depending upon the user's requirements.
PCBsMy pal who does PCB designs for me was here yesterday. I have commissioned a Mk II PCB design with exactly the same control/screen layout as the Mk I he produced back in May. The cunning plan is to piggyback the Arduino onto this PCB, behind the display, so that there will be no physical wiring at all apart from the USB cable to the Arduino and HDMI cable to the display. This will make the controller very neat and easy to replicate. I expect to use the same approach for any other PCB layouts that I commission.
This is all very much a work in progress and I suspect it'll be Christmas before I have anything to look at. In the meantime the Mk I controller is doing a great job as my main station radio.