I don’t think that the OSSC needs to be this product you are after, because they already exist.
If you want to use the OSSC as upscaler with GC, use GCVideoLite for analog YPbPr (or RGB).
If you still want the GCVideoDVI for HDMI output, let something like a DVDO unit do the upscaling. Or simply your TV…
Also, there are dual versions of the GCvideo board coming out in the near future anyway, so you don’t even have to choose.