the 5dc was very difficult. alex and i basically paved the way for future VxWorks cameras though (look at the 40D port, it wasn't too difficult i don't think).
But yes, the main problems are lower resolution display (had to make the menu and printing and everything scaled down to fit), different boot code, and sometimes limited memory can make things slow.
I think the whole 1D line is out of our typical "userbase market", so not sure how other devs will feel about porting this (probably not many will step up to do it).