I think they would have already announced that, if Varl was to be included. There's no way they would have left out a planet if it's on the way with Makeb. At best, there might be a quest that takes you there briefly, but I don't think Varl is coming in the expansion.
Varl, whilst an explorable world, would be more of a new dailies area like Black Hole and Section X. They still have more to reveal about the expansion, there's still hope that it could be that.