Scratch uses the nVidia Quadro SDI board for SDI output (Windows only since there are no Mac drivers for the SDI daughterboard).
I don't think you should expect Scratch to use other SDI boards anytime soon. This is what I infer from informal discussions on the Assimilate user group. Scratch is aimed at super high realtime performance the Quadro SDI daughterboard pipes the video directly from the GPU to the SDI output. Using another SDI board like AJA or BM means the data has to be sent back over the PCI bus into another card which can clog up the PCI bus when working with high-bandwidth material.
At IBC Assimilate announced the support of the Aja Kona3G for SDI on the Mac platform. This is not to replace the nvidia (Scratch is still GPU based and uses CUDA) but to fill the lack of nvidia SDI daughter card on Mac.
The guys have been working hard on that and, as Barend mentioned, achieved to send back the image from the GPU to the bus for the SDI out in realtime.
Thanks so much for this info!!!!!
Interesting times, I hope they expand the output lines on the mac to include Lhi and new thunder bolt based hardware over time cuz things are changing quickly. With adobes new acquisition, da Vinci expanding quickly and marketing aggressivly