With the new Galactic Legends characters of Rey and Kylo Ren being announced the question is... exactly how will they be unlocked?
At the moment we have multiple "event" type characters out there.
Legendary: 5* unlocks with specific factions
Journey: 7* unlocks with specific named characters
Epic Confrontation: 5* unlocks with multiple specific named characters
TB Specific Mission: ROLO, IPD, Wat, KAM
GETMk1: HYoda, Wampa, Remaining shards for Malak and GAS
GETMk2: Negotiator, Malevolence
Achievement: Darth Vader
They had talked about, what feels like ages ago, adding in more ways to unlock characters. I feel this definitely falls into that category.
Which leads to my speculation...
I believe the GL Reylo will be unlocked after a quest line is completed. You will have to work on specific milestones in-game that will be checked off and then you will unlock them. What those milestones are... who knows. Maybe getting the whole Resistance and First Order factions to a certain gear requirement or perhaps just merely unlocking them all?