Yeah, the next one will be in 2019. Not sure why though.
Probably to save a lot on convention costs internationally and they will probably keep it in the states, likely Anaheim, to coincide the launch of Star Wars Land opening in 2019.
That's my guess. More anticipation and build up in-between not doing them every year and so they can keep aligned with promoting the episodic Star Wars films the year of each convention.
The other possibility is they start bleeding these in with D23, but I doubt that since Star Wars is proven large enough to have its own convention.