BTW, I didn't see this in the release notes anywhere (apologies if I missed it), but on the Song Details -> Regions tab, there is a new Waveform Source button that let's you select which individual audio track, or All Tracks (Mixdown), to use for the waveform.
The other possibility is that this a partially implemented new feature that snuck through 🙂
While it re-draws the waveform based on selected track, playback is still combined mixdown (I know some people were asking for both waveform AND audio to be a specific track).