That's it, I don't have much more to say :)
A couple months ago, given the feedback I received on the project, I decided to order a batch of 20 Micro:Gamer from Seeedstudio. They are now available on Tindie.
The hardware is 99% the same as revision B, I only moved some components by a few millimeters and added more decoration on the silk screen. Also the PCB is now red!
On the software side, the Micro:Gamer library is integrated in the Arduino library manager. So it is even more easy to start programming.