Unfortunately progress has been a little bit slower than I expected, I wanted to have a couple of weeks off from the development as I have been developing the service almost daily this year. After that my full-time job has been quite demanding (travel, etc) which meant that I have not been able to progress as much as I would have wanted.
I have begun to implement credit system for the service, but I have not yet had time to focus on the Mac synthesizer host application.