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.