While in game, her story line hasn't moved forward since vanilla, I believe her background lore has been set up quite well. As the theory goes, the stranger was one of the researchers in the ishtar collective that got trapped in a vex mind. Once they escaped, they began exploring the vex network and have thought to be stopping calamity by influencing what were once established events. Why, just look at how her influence shaped our fledgling story. Tl;dr: If she happens to not show up in game, she'll probably get some vague links in the grimoire. I'm personally interested to see if she'll show. Both possibilities provide interesting paths for the lore

Well we know that at the planets of destiny 2 their going to be npcs spread around put i doubt it that bungie would put her as an npc without a cinematic reveal since they said that they are gonna put more cinematics in D2 i think the chances of the exo stranger appearing in D2 are very high and if not we can still hope that she will appear at the osiris dlc since Osiris is interest in the vex and the stranger wants to stop the vex so they got that linking them,or any other future dlc with a name that is related to the exo stranger that bungie haven't told us