Power Rangers is in theaters now (and it's not that bad), and Saban has very big expectations for it. Not only are they already looking forward to a possible six-movie series, which is hugely ambitious, but they are already beginning to tease that future.
You'll note that one of the Rangers that does not appear in all of the promos is the Green Ranger, and there's a very good reason for that which I won't spoil. Be sure to stick around through the credits, though. Anyway, the film's official Twitter has gone ahead and teased the future arrival of the Green Ranger, one of the most complex and popular Rangers of all.
Tommy Oliver (Jason David Frank) was the guy in the Green Ranger suit, who made his debut on Mighty Morphin Power Rangers way back in 1993. The evil Rita Repulsa enchanted him to make him her servant, and granted him the ability to transform into the Green Ranger, with powers that exceeded the others. After doing considerable damage to the team, he eventually overcomes Rita's spell and joins the team as its sixth member. Tommy would soon become the White Ranger, followed by multiple other Rangers over the course of numerous series. He is considered by many to be the greatest Ranger of all-time, and within the context of the show is seen as a legend.
So this was bound to happen, and if Power Rangers lasts as long as hoped, we'll likely see many more versions pop up.