Steven Universe. Star vs The Forces of Evil. Rick and Morty. Transformers. Gravity Falls. Avatar: The Last Airbender. There are plenty of options for alternative content to include with varying degrees of tying or fitting in to Ponies.
There are only three real stipulations that I think need to be enforced with selecting non-pony material. Bear in mind these rules are my Opinion so feel free to argue about them:
1) With the exception of dubbing due to the VAs, Anime, Manga and Comic Book stuff isn't involved at all. There are GOD knows how many Anime and Comic Cons throughout the United States for people to get their fix of that stuff, and there's plenty of OTHER material out there to include.
2) No live action stuff. Having panels based on live action media would oddly clash with the cartoony theme of the rest of the con (Exceptions for things that tie into ponies, of course)
3) Non-Pony content is SECOND picked to Pony content. Meaning that if we have enough event material for a full Con, we don't need non-pony stuff to be put in at all.