@matigo Sounds like you're expecting one repo per account?
The release thing sounds really weird and heavyweight. It also is the only thing that really ties you to GitHub. I'd expect something like "master mirrors to 10C" instead.
Putting media files in the repo should probably not be too bad for just images. Might blow out GitHub's repo size limit with lots of audio and especially video.
I'd kind of think the media should be off in a separate assets folder that all the sites can reference, but that's probably way more awkward than dropping them in a folder alongside the primary user of the file.
ETA: I'd probably not use this and just stick with publishing through the Web interface. I'm pretty annoyed with having git as part of my publishing process for my own personal blog already, though that's hard to untangle from also being annoyed with Octopress and Ruby standing between me and publishing.
How would post preview work with this new system for 10C?