Naturally, the first thing people can run to is that he'd play Stephen Strange himself. I can't quite see that happening. We here at Fanboys Anonymous recently did an edition of Fanboys Cast for Doctor Strange and in retrospect, I still can't see Ramirez being a better fit than anyone we suggested.
Clearly, Ramirez would not be playing Clea, Wong, or The Ancient One, so that doesn't leave many other options to choose from. If he's playing some extra character they created specifically for the movie (à la Darcy in Thor), then that would be virtually impossible to predict. However, if he ends up being someone noteworthy from the comics, then the possible roles are limited.
Dormammu and Baron Mordo seems like the most obvious choice for a villain duo in the movie, to the point where it'd basically be ludicrous to do anyone else. Ramirez has enough of a resemblance to Karl Mordo to be able to pull him off, not to mention that he's right at that popularity level where he's somewhat of a name, though not big enough to be a huge paycheck. That's a big bonus for Marvel to go after, rather than targeting someone like Joaquin Phoenix, who has been mentioned numerous times in fan casts for the part.
That being said, this could all be total nonsense that leads nowhere. There's nothing to indicate that any contracts have been signed, nor have there been any official announcements. Until then: