On a related note, this might be useful for someone looking at an MTK bootloader. I don't believe this code is in most of the leaked SDKs, but I've see it on pudn.net...
http://rapidshare.com/files/377689884/mtk-bootloader.tar.gz.html
There might be a couple other versions floating around as well. I can check for them if people are interested.
Still I believe it is feasible. So if you want to stay out of the GSM part, feel like the Calypso is too boring for you: Why not work on getting a minimal custom software image for the MT622x running, including bootloader support,
I don't know anything about microcontroller development, so I can't be much help there I'm afraid.