A rather long but interesting video on just using the Sun to remove yellowing:
He’s talked to a bunch of smart people (one is a Chemist that looks into plastic degradation issues for GE Global research) in researching this video.
I like that he cuts deep into some plastic keyboard keys to show how deep the yellowing goes (not deep at all) and tests how heat also affects yellowing. The heat, I think, would explain how a Dreamcast case I retro brightened re-yellowed within a few weeks despite being left in a cupboard.
Seems the downside is it takes a lot of time but no disassembly or making the plastic more brittle like with other retro bright methods. Also, it appears that the more you repeat the process the more resistant the plastic becomes to re-yellowing.
A UV blocking wipe was mentioned (only works on surfaces that have never yellowed) which could be a good way of preventing it on consoles that are still in good condition but I get the feeling it might leave a surface glossy?