Talk:Twilight's Kingdom - Part 1/@comment-188360-20140416182813

So, the Hub has issued a press release about this episode and the second part, along with an image from it. It does confirm that "all the princesses" does indeed include Cadance.

http://press.discovery.com/media/ugc/press/My_Little_Pony_S4_Finale_Release_Final_4-16-14.pdf