This is already on the 'ideas' list: http://forums.adobe.com/ideas/1446
Make sure to add your vote there if you haven't already.
Unfortunately there's no ETA for this.
We have also updated the Getting Started with Adobe Muse (Part 7) tutorial to include information on how to approach consistency in your design across multiple devices:
Please please please make Muse ready for all devices. I didn't realize it wasn't already incorporated and instructed all my designers to use Adobe Muse from now on.
Now I see the pages don't scale nicely on Android and iPhone at the same time. This is horrible for me and my company, most of the internet traffic nowadays comes via all channels.
I have to consider hiring mobile specialists next to my webdesigners now :-(