I have my Apple Watch set up to use the Soundtouch app. There does not seem to be a way to make it appear as part of a watch face, but it does show up in the app "cluster" that I get when I press the watch stem.
However, the only speaker that I am able to control on the Watch is my WAVE radio. If I make the WAVE the master device, and add any or all of my other speakers, I can control the WAVE - but not the Group - volume. If I use my iphone or iMac to start the WAVE, I can get the WAVE, and then the Wave Group, to play any of my sources. But on the Watch, I can only invoke one of the six preselects I've established, and if I start (on my iphone) using some other source (say, Spotify) I can only switch to one of the preselects - and I can't switch back to Spotify.
I note that the WAVE is the first speaker I established in SoundTouch, so my guess is that if I go to the trouble of reordering - meaning eliminating then adding back - my speakers, I could get some other speaker to be the one my Watch can control.
So it appears to me that the Watch version of SoundTouch can only control the sound on the first speaker added to SoundTouch, and is limited to switching to one of the presets. This means that there's very limited utility to the Watch version of SoundTouch - from a practical point of view, it is only useful if you are in the same room as the pre-designated speaker, and then only to control the volume & select a preset.
Am I missing something? Does Bose have any plans to integrate more completely with Apple Watch? Will Airplay 2 make a difference?