Openchrome supports all VIA IGPs, unichrome only supports few of them. Also, XvMC is a key feature, especially when attached to a low power but also low consumption and low thermal envelope CPU.
Hrm... But what were the important things you said are highest on your TODO list again? Aren't those a really close match for what i wanted to achieve with unichrome and the things the people who ran to opechrome refused to prioritise as such and therefor forked away?