Cortana has been around for a while now (Since Win 8 I believe) however I never played with it much.
Since Windows has been developing Speech recognition for several years you'd think Cortana would be light years ahead of
Siri, Alexa, Google.......
Sadly Windows never used the clouds processing power until Cortana.
Recently I started looking at Cortana a little more. There are even skills for her though not as many as Alexa or Google.
There isn't anything yet for X10 directly but there are skills for the Wink, Smart things, Insteon, Philips Hue and other hubs.
Again like the other Voice assistants many things are only available in the Unite States
It makes sense to enable Cortana and utilize her for when your at the PC even if you use another Voice recognition enabled Program.
Since there is a software developers tool kit (SDK) for Cortana for creating skills as well as integration with other apps I may look into doing something with her ( If I don't to confused and lost in the documentation)
I think you should be able to get X10 working with a RM Broadlink and Smart Things since a hub isn't required for Smart Things
For now I'm interested in how others may be using her and what skills your using.
Also If you've got Cortana controlling X10 please share how you've done it.