Make sure your RetroArch works, this is not an Emulationstation problem. Also, this is a RetroPie forum, not a general RetroArch forum - you might want to try the libretro forums if you have problems using RetroArch on Windows.
Well im currently working on this...The .cmd file used to download windows 10 for arm is super sketchy mostly because i havnt really looked at it, but does seem to work.
It took about 4 hours last night just to download the files required over a 250mbit connection so its odd.
Follow the instructions here: Github
On first boot it dropped me to a UEFI shell, but you can get into the config by hitting esc as it boots and select boot from file selecting bootaa64.efi in the boot partition. Not my first rodeo on this so i figured it out quickly.
40 minutes in im still sitting here at the first boot screen "configuring devices" it by no means is fast, but it actually does seem to boot.
EDIT 1: I believe i broke it lol After a couple hours of it sitting on that same screen with the wheel spinning i pulled the power from it and was presented with message stating "blah blah hit ok to restart the computer and restart the installation" Its an endless loop though so ill have to start over :(
EDIT 2: Started over from scratch and there is some randomness to that cmd file which im not liking...I had to keep hitting enter for a few hours while it downloads, extracts, and compresses its data where it left me with no files to work with then on the 3rd run of it i did not and actually got the iso the first attempt gave me. Ive been at this all day and still have not tried my second attempt due to the time sink on this, but will get to it again tomorrow morning. I also think that the SD card i used was trash so my next image (currently writing to disk) will be on another...
EDIT 3: I gave up. It ran and i got it to boot to a point where it BSODed on me 3 times in a row complaining about drivers (no surprise here!). I also went through the logs and found "out of memory errors" on loading xyz and wiped the SD Card...as it turns out i gave up too soon according to this as thats to be expected, but not worth the time invested: Toms Hardware
Can you run windows 10 on a pi? I guess... but should you? no!