A topic that interests me is if V4L2 API can be used to drive professional broadcast level SDI hardware.
As far as I am aware there is nothing special about SDI. It should be trivial to use the V4L2 API for it.
I've worked on a HD-SDI driver before (not a linux driver, though) and it's all fairly simple.
By this do you mean the V4L API as-is supports SDI or, in your opinion, we need some changes?