I'm still using this keyboard as my everyday main keyboard, and of course there has been some development in the mean time.
I've made two more modules for the center, and a "blank" one to just make it look better. I also replaced the buttons on those modules with buttons specifically made for mice, so they have the exact feel and click you know from clicking your mouse button. It seems like a small thing, but actually it's a huge improvement. The module with the silver knobs is a joystick and a scrollwheel, and both can be pushed down for clicking too. They are not particularly convenient.
The last thing is a "trackpad" module from a smartphone that I am working on at #Home Button for Keyboards project — when I get it working, it will be another module for this keyboard.
There have also been some other changes. I swapped the Ins and Del keys with the bracket keys eventually, so that they are on the same hand as on regular keyboard — that works better for me for copying and pasting. I also moved around the media keys (used witth the Fn key) to make them easier to remember. Oh, and Fn+Tab is now Compose.
I also added the improvements that came with the new version of CircuitPython — matrix scanning done in C using the keypad module, boot.py disabling the USB drive and UART console unless a key was pressed when booting, and custom HID bitmap NKRO reports.
Finally, I've also sent one spare PCB to a person interested in building this — haven't heard what they built with it yet.
One thing that I hoped to do was replacing the keycaps with the MBK Legend ones, alas, the group buy is delayed and they are still working on producing them — the current estimate is shipping by the end of the year.