The trend in website design is responsiveness. I use mostly Adobe Muse and that is why I ask: "What is the use of an adaptive XD for Muse-users because responsive design is the word of the day"? I design everything by using Muse and I can see results immediately in responsive format with all breakpoints. In my opinion XD is a great tool but is it coming too late?
I think you'll see significant divergence as XD grows into its purpose: design and prototyping. From the very beginning, Adobe Muse was about allowing people to create their own responsive websites without having to handle all the breakpoints themselves. Adobe XD is focused on allowing designers to be able to quickly design and prototype. As you take a look at our roadmap going forward, you can see we're heading more toward allowing designers to quickly iterate on their designs, in everything from microinteractions to realtime design previews.
Hope that helps clarify things for you!