Reading the iOS 9 forum on macrumors I thought the same thing. Since there will be a new icon for Apple Music on iOS (with the 8.4 update), What about Apple Watch? I saw a picture of the AW with the new music icon on the apple website, so wouldn't there be an update to watchOS?
^^ Hadn't thought about that, but it does seem then that we will be getting a (minor, from the sounds of it) Watch OS update sometime tomorrow, or in the very near future, as well.
I wonder what other potential updates/bug fixes may be included as well!