Advert enhanced start menu
Having seen what MS did with solitaire in windows 10, I wouldn't be surprised to see them add adverts to other parts of the system. In addition to the massive personal data slurp they've already put in.
Cortana will defiantly have them - it basically does already courtesy of bing.
I can see them slipping some adverts into the new start menu - removable, of course, by subscribing to office365 or windows365