I just opened the Preview portal and was welcomed by a small guidance wizard with a quick tour. After that I noticed that there were some new icons and that the +NEW menu got an upgrade as well.
So in the main menu there’s a new add-ons item:
And in the +NEW button on the lower left there’s also the new feature “Store”:
However when clicking it I got the message:
That’s a bit of a bummer so I guess I’ll have to wait before I can make use off the new things being provided here. I have a good feeling that next week Microsoft will reveal a lot more about this during the BUILD conference.