Actually, I can't agree that it has downsides. It's consistent with the rest of the UI and it's informative-- what are the downsides of that?
"I don't need the active button to be highlighted when I can see there's text being written"
You don't? You either pay very close attention to the window or you must be in very quiet channels. I don't watch every line going into the window or keep bookmarks in my head of where I left off, so if I turn my head for a few minutes I could easily miss a page of conversation and not even realize it. I'm sure this has happened to you at least once.
