I am surprised that no one has said this on here...
Virtual Assistant. Think Cortana except its actually a person. This seems like the most likely thing since it is built on Win 10 anyways.
my next idea was a Haloworld. You can essentially create things in your own Haloworld and place them anywhere. You would then control your access rights to your own Haloworld (like file sharing) and could allow others to see your projects. I would imagine there to be a public domain as well where if you were to walk outside, you would get bombarded with marketing, sculpture graffiti, and other crazy things. I am just picturing two people playing with a virtual dinosaur on the corner while the Superbowl lights up the sky, all the while I have my own person walking musician walking next to me.
As an engineer, the design ideas are endless with making catalogs of parts available from online services managed by the vendors, suppliers, etc...
Cooking instructional demonstrations in your kitchen (and virtual cataloging so you don't forget where everything is).
Interior Design studios from manufacturers... I.e. How is that couch going to look and fit in my living room...
Virtual speeches/press confrences...
I could go on...