That was most certainly a thing. Now the question is, what kind of a thing was it?

On the one hand, we now have all sorts of things that have become canonical. Yes, we already had "Alicorn" in show from Magic Duel, but only with Magical Mystery Cure do we have a confirmation that Alicorn is used to refer to Winged Unicorns.

On the other hand, Twi is now a Princess. A princess with stewardship over what, exactly? Celestia has stewardship over the day, Luna over the night, and Cadence presumably over love. How can Twilight be a princess and not be the princess with stewardship over magic?

Also, what do you think the odds will be that she'll fall in love with a plumber from Manehatten?