I've been thinking about similar stuff to what Cohh mentioned about him being able to click on a chat message and it popping up on stream so it's visible when he answers it...
My idea is a smart system that rates by words and emotes, perhaps like an addition to sub-only mode if needed, that de-emphasizes non relevant stuff during peak, and highlights relevant stuff better, maybe has a separate scroll section for high scoring messages so it doesn't scroll off screen so fast with 10k+ viewers... It would likely require a lot of tweaking during testing, but I think that if Cohh has both the regular chat and the SmartChat (or whatever) to help him not miss stuff he'd want to see, then that's a good thing.
/Tanek