Just wondering if there are going to be rules for this. Force & Destiny seems the likliest place, since it's origin is as an anti-Jedi martial art.

Nothing as of yet.

Hired Gun was a lot of folks' bet for when we'd start seeing stuff relating to various martial arts in the Star Wars setting (and there's a lot more than just Teras Kasi), but that ship has long since sailed. Possible we might see martial arts stuff in the eventual Commando source book for Age of Rebellion. Or it could be the Warrior sourcebook once Force and Destiny has the final version released.

FFG plays with their cards held very close to the vest, and we typically don't hear about much about upcoming releases beyond a "hey, this cool new product is coming in a couple of quarters!" until the book's just shy of hitting store shelves.