Well one possible plot line I could think of is that Ryder goes to the background as the celebrated Pathfinder that made settling in the Andromeda Galaxy possible.
But then the Kett attacks keep happening and there's talk of a massive invasion. As we don't have the resources to defend against the full might of the Kett Empire, we take the fight to them.
So a new hero stands up that is part of the attack and when the attack fails, he/she is left with a single small ship and crew to go inside the Kett main base to try a final suicidal mission that will at least cripple and halt the Kett.
While we do this, we find out some more about the dreaded Scourge which turns everything we knew upside down.
End of that chapter. More to follow.
Now if the new hero gets sequels, I could be ok with this being a one-off but I really don't want to go from one one-off to another like DA.