The issue is going to be drivers and if the Win 7 will work with the Surfacebook.  I know people of have downgraded a Win 8 machine to Win 7 and that didn't go as planned (lots of driver issues).  It appears there are several people over at the other forum that are running Win 10 with no problems.

I am also looking at getting a Surfacebook in the next week or so.  I am going to run it in Windows 10 though.