Evidence has been mounting over the last few days and it looks like it's finally happening: Android 6.0 for Wear is starting to roll out. Googler Wayne Piekarski just announced on his Google+ feed that OTAs have begun and should continue over the next few weeks.
An official blog post by Google lists some of the new features we can expect in the new firmware, including: newly navigation gestures, audio support on speaker-equipped watches, and expanded support for messaging clients.
The update itself seems a bit 'eh', but the interesting thing here is that all Android Wear devices will be getting this update to Marshmallow, even the first generation Wear smartwatches.
Goes to show that Google does, in fact, know how to do this - now they just need to apply this to phones and tablets.