I also am a software developer, and was thinking of looking up how to hack into the internals of Mainstage to accomplish this.
So I am very interested in how far you have gotten, and if you need a co-collaborator to help move this forward, let me know.
I also will look into how to do MIDI scripting as Mainstage supposedly supports.
@SRF_Audio, I saw your tutorial recently and was wondering the very same thing, about why not just use Logic alone if you are going through all that hassle anyway. I'm thinking about that option as well, although I'm wondering, is there a nice way to switch songs quickly, or is it literally file->open->choose next song->wait for it to load->go?
Glad to know switching to Ableton isn't such a wonderful solution, because I hate the look of the interface and it would really depress me to have to go down learning that path