Deja’s portrayer being upped to a series regular in Season 3 certainly adds to the potential that she could have a role in that future-set story.
Whether or not the flash-forward storyline involves Deja being revealed as “her,” this bit of news certainly does not rule out the possibility she could play a role in the future.
This Is Us creator Dan Fogelman recently revealed that the mystery surrounding the flash forward sequence would not go on for multiple seasons, hinting that there will be answers given over the course of Season 3.