Well, there were quite a few bugs in the device and it looks like the baseboard is going to redesigned, although it will still be compatible with all the extension ‘shields’.
It looked like the transistors gave a .2 volts voltage drop, and the diodes dropped 0.1 more, turning regulated 3.3 into 3.0 volts, so sot-23 mosfets are already on the way.
Meanwhile, I started to write some software. This resulted into a dumb commandline utility called muart-ctl.
And… A KDE4 Plasmoid, that acts as a frontend.
Here goes the obligatory screenshot: 
And the full shot of the desktop: 
Profile management is not yet ready, and there are still some issues in the electronics, that need further addressing (And a new PCB!), but nevertheless it works.
The plasmoid is written in javascript, which was kind of pain. The bindings are not well documented, so I had to do quite a lot of guessing. Nevertheless, as for my first javascript project it all went fine. Lots of thanks to Nikita Melnichenko, for the plasmoid ‘makeprogress’. I tore that one apart and used as a reference.