I’m a streamer for Super Smash Bros. Melee. If hardware allows, taking a 480p signal and converting it to 480i (with no frame buffer/lag) would be a great feature that would improve my video quality. I want to be able to output 480p through HDMI (GCVideo) while the component output of the GameCube is put through the OSSC and converted to 480i. The reason why this would be necessary is because the competitors will be on 480i CRTs, and cannot handle 480p. In my current configuration, best I can do is output 480i over HDMI and deinterlace/scale through the framemeister. This feature as a whole would really only benefit some streamers, but it would help me out in my specific case.
I was wanting to do what you’re wanting a while ago, and I ended up getting a setup that could do it. It’s not easy though!
If you want something that can do exactly what you want, take a look at the Extron Super Emotia – http://retrorgb.com/emotia.html
It’s an Interlacer that takes 480p VGA and outputs RGB 480i.
You’d probably need an Extron RGB in the chain somewhere to clean up the signal and allow you to tweak it further though.
What I will say is that the end result is great, lagless playing on a CRT with a 480p output for streaming.