So I saw in screenshots in another thread that, on the Mac, the section of the System Preferences app that tells you which apps are using iCloud storage now lists Messages as being one of those apps, and that wasn't there before. Apparently checking and unchecking this setting doesn't do anything yet, but I'm hoping this means that real cloud syncing is finally coming to Messages. I was definitely annoyed that they added all the emoji stuff at the expense of this kind of (pretty basic, IMO) feature, but maybe they didn't! Time will tell...
here is a link to that thread.
If anyone who has access to iOS 10 beta sees any similar or corresponding setting, I'd love to know!