CG has confirmed JTR's return on June 14th Link
JTR confirmed to come back March 15th. Event has been added to the official March calendar. Yes, the event is back early compared to CLS. There's still a chance that it could return again in April/May.
If we look at the the CLS event, there is 140 days between when CLS first came and returned. If we look at JTR, 140 days from Dec 15th is May 4th. Coincidence? Maybe.
We are estimating that Rey's Hero's Journey event will return sometime in April. This is 4 months since the event first happened. This is based on Luke's Hero's Journey taking 4 months to return. The 4 month timeline is an estimate; CG can and will change this as they need. That being said, if you really want to get RJT, then you should start farming the required characters now.
It is confirmed that the event will require Rey (Scavenger), Finn, BB-8, Veteran Smuggler Han Solo, & Veteran Smuggler Chewbacca - all at 7 stars. This will unlock Rey (Jedi Training) at 7 stars.
BB-8 is returning on 2017-12-08.
Vets will be farmable on Cantina nodes starting November 22
Few details are known except that there is a Rey's Journey and Rey (Scavenger) will be needed. The event was said (by CG) to start with the theatrical release of Star Wars™: The Last Jedi this December.
Lots of rumors that BB-8, Veteran Smuggler Chewbacca, Veteran Smuggler Han Solo, Rey (Scavenger), and Finn will be needed at 7* to unlock a new Rey character
If this happens, the BB-8 event will return in November/early December