Separate regular Chat and Highlighted Message chat.
So, my issue with Highlighted Messages is that almost all the time they get drowned out by the other messages anyways, especially with larger streamers. The whole point (To my understanding) of highlighted messages is to make them more visible to the streamer, which often doesn't happen for the reason I stated earlier.
So here's how I think this can be improved: Separate regular chat from Highlighted Chat. This way the highlighted messages won't be drowned out. Even though the cost, and by extension the frequency of Highlighted Messages will vary and could be low OR high, it still won't go by fast enough to be missed completely... most of the time, at least, and while they still might not be seen right away, they WILL be seen eventually.