I'm not sure if anyone is still interested in this topic. I had the exact same idea. I'd LOVE to get something like this sorted. So much so that I'm reading through Programming the Nintendo Game Boy Advance by Jonathan Harbour. The links people provided had lots of information, but I think if I'm gonna make this happen, I need to start from scratch.
I'll let you know how I'm doing with it. Hopefully have a proof of concept together before too long.