So, some confirmation: It seems as though you can control your phone from the watch, but not browse your library from your phone like before.
Apple Watch Series 2 (watchOS 4 beta 4) + AirPods + iPhone 6s Plus (iOS 11 beta 4)
Music:
- I start playing a song on my phone, it shows up as "Now Playing" on the watch, I hear it on the AirPods.
- this doesn't always show the actual track playing, but I think that's because the phone doesn't always show the right information on the Music Widget / lock-screen view, an issue with the beta
- I can also choose a playlist/track that has been synced. Choosing one of these playlists prompts me to select the AirPods.
- The AirPods aren't always available with just the watch. They don't seem to like the beta OS on watch, phone, or tv, so sometimes autoswitching fails, but is better on the watchOS 4 Beta than OS 3
- When I start playing music on my phone or watch, the Now Playing view shows on the watch screen automatically.
- This is a setting, but even when turned off, "Now Playing" shows when I raise my wrist
- When I have my AirPods connected, while playing music from my phone or watch, the Digital Crown controls volume
- done in the Now Playing view, based on your settings, either raise your wrist or wake the screen by tapping without looking
I use Gymatic for most workout tracking (besides RunKeeper for running), mostly using the "Freeform" mode that detects the exercise and reps. I usually get music started first (siri, workout mix playlist), then launch the Gymatic Freeform workout and let them both run for a couple moments before getting started. Double-clicking the crown switched between the two apps (Music / Gymatic) because I occasionally need to confirm details on the exercise between sets and the Music apps doesn't take over on wake while working out, so adjusting volume is an extra step.