This was true in previous versions, but with the Fall Creators Update you can mount mapped network drives inside of Linux:
sudo mount -t drvfs z: /mnt/z
Now that's pretty cool. It even works for removable fat32 media!
you know, i just noticed this... my ExFAT SD Card is not visible... hmmm....
I think this is because WSL uses NTFS Alternate data streams to store linux file attributes, and they don't survive when a file is copied to a non-NTFS file system.
No, I don't think so. Alternate streams are only used inside the emulated Linux filesystem, not externally.