More precisely it will once Android Wear gets bumped to Android 6.0. Seeing as Hangouts has Its own Wear app it makes sense for Messenger to have one especially as not everyone is using Hangouts to carry their SMS requirements.
Only a few weeks back Hangouts had an update and in that update was an option to try Messenger. Many reckon that SMS will be removed from Hangouts.
Either way Messenger is my way of doing SMS and a dedicated Wear app is long overdue. When it does show up it'll be a scaled down version of the current app very much like Keep does.
There are some hardcore fans of Hangouts out there who won't want to see SMS go but whatever happens Google needs to get something done and stick with it.