If they release a Surface phone running full Windows 10 64bit OS it would be aimed at business users and be at a premium price. It seems a nice idea, but the market for such a device is limited. Surface tablets are nice but they haven't exactly flown off the shelves due to the premium prices. Surface Book looks amazing, but I haven't ever seen anybody using one in a coffee shop yet.
I tend to see Apple, Dell and HP devices and my Linx 7 being used.
I do have a Lumia 435 which I use for fun and testing out, Windows phone isn't bad, Outlook and Office work well but app support is very poor.