Having seen the Dimensional Vortex video, and combining that with what little else I know about the series (compared to someone who actually played Cross and got endings besides the Dream Team) I'd say we might witness the creation of the Time Devourer. The Prophet and Schala both have blue hair, so I don't see why they wouldn't use the prophet's back sprite for Schala wearing a hooded robe.
Perhaps if the mysterious figure turns around or otherwise reveals itself, it might turn out to be Schala, or it might be the Lavos Core in disguise. Of course, it could be Queen Zeal, back from the dead, ready to merge with lavos and destroy time, only to be eaten by the Time devourer because Schala beat her to it. Or it could be Queen leene, Lucca, or Crono's long-lost brother who actually talks. I'll leave it to the reader to decide which of those sentences is a joke. My point is, you just never know.
Regardless, my money's on Schala merging with Lavos, and that is where it will stay until I am proven wrong.