Does it have a good terminal emulator ?
The one(s) that come with cmd and powershell seem pretty terrible..
My favorite terminal emulator under windows is the native rxvt from cygwin, much to my dismay is no longer available in cygwin (you have to use X now), I asked the developers one or two years ago on that since there was no mention on the site and they said it wasn't maintained anymore and they couldn't update it or something. So I just keep the old cygwin around for as long as it keeps workin.
My usage of cygwin is pretty limited to basic command line stuff and ssh. Without rxvt though it would be quite a bit more painful, and running full X doesn't sound appealing just for a few terminal windows. Cygwin user for a good 16-18 years now.
I struggle to think of use cases for this subsystem but come up mostly empty. I browsed Scott's blog posting on the developer aspect and it sounds like it could be useful there, though not for me since I am not a developer.
I'm sure a Linux subsystem is quite a bit less overhead than a VM though systems are so powerful these days, so much ram and so many cpu cores, even laptops that for most folks I think they are better off with a VM where you can back it up easier, experiment more(if needed), take snapshots of the VM and things like that.
I was running the earliest versions of vmware (pre 1.0) back in 1999 with windows on top of Linux at the time. Those were days of constrained resources for virtualization on the desktop. I remember trying Bochs too with Win9x, which worked as long as you were comfortable with 30 minute boot times(or so it seemed like from memory).
Windows 10 has so many downsides to it I can't imagine anything they could put into the system that would make me want to upgrade from 7.