Tomorrow, my 5Dc will go to its rightful owner, so... probably it's time to post a
beta 4.
It was compiled from the same code base used for
7D alpha 1, it feels quite solid on my 5Dc (although I didn't shoot anything serious with it, just ran built-in stability tests that simulate random button presses), and it basically contains all the features I could port without significant reverse engineering efforts.
For more stuff (e.g. bulb exposures, trap focus or shutter count), one should dig deep inside the firmware. None of the tools from my current arsenal was able to find those, so it's probably hard - probably as hard as the 7D port

Auto ISO needs to be implemented from scratch or ported from 400plus. For me, the only auto exposure that I consider good enough is the one that exposes to the right. And from what I know, this is not possible to get with current hardware outside LiveView - not even on 5D3. If you disagree, just tell me how

That's it - the 5Dc was quite fun to analyze, lots of internals are simpler and can be understood, but... it has some severe limitations. ML code is open, there are both
free and
paid reverse engineering tools, anyone can look inside and continue to experiment, there are firmware addons for 350D and 400D from where you can learn and borrow features... you only need time, skills and the desire to innovate.
I hope this update will effectively turn your 5Dc into a new camera (well... without LiveView).
Enjoy!