I think the One U.I 8 watch only supports respond replies in messenger same in current One U.I, most watches like the apple watch and other smartwatches doesn't have the messenger app that you can litterally download in the watch (correct me if i am wrong) maybe in future gen they will add it? Depends on the users demands, but still its Samsung decision to add it or maybe you can have a feedback to them in you're idea.
