a) only 32bit
b) At what speed though? x86 emulation isn't trivial, and arm seems to be sufficiently different in architecture to incur a large translation overhead.
Microsoft has had videos out for a while of their x86 emulation. They have a demo of loading Photoshop CC, and it looks close to native speed, though I notice a bit of window refresh. Looks usable, but I'd like to see more demos.
Not only that, but if you are making UWP packages (for the windows store? I'm not sure if they are standalone as well), you can ship both x86 and ARM binaries together. I'm probably butchering the details, but the presentation and accompanying HN discussion was interesting[1]. The video is pretty cool, as they demo real running x86 and ARM binaries on the same system, and explain some seriously cool stuff WRT x86 emulation.