I'm intrigued by this as well. My laptop just died, so I need a new one. Not primarily for music production, but that would sure be nice for whiling away time in airport lounges and hotel rooms. So I did a little googling.
Interesting stuff
here. They seem to take it seriously as an audio production platform. The tiny touchscreen would drive me nuts, though. I currently have two 22" monitors and sometimes it feels cramped. My now-retired laptop had a 17" screen and that felt small.
Here's a guy who ran ProTools on one. Both sources say they use ASIO4All, but nobody explains why. I can only assume they're using the computer's integrated audio. But again, why? He ran with a 512-sample buffer, but doesn't say if that was as low as he could go, or if he just picked a conservative value to start with.
Microsoft claims it's a legitimate audio platform, specifically mentioning ProTools, Ableton Live and Cubase. But there's a video of a guy using Reason that isn't selling me at all, watching him struggle with microscopic controls on plugins and two-fingered function keys. He's also using ASIO4All, even with an external USB interface.
Then there's the price. The Surface Pro 4 is $1000.
Much less than I paid for my recently-deceased HP laptop, but a few years have passed since then and $1000 is now on the high side. Comparable laptops can be had for half that.
All in all, my admittedly minimal research has pretty much put me off the idea of a Surface Pro.