He took Al's file, so I assume he's going to go after him. But you're right that it doesn't seem like that interesting of a story.
The "good father" story was already done with Trinity, unless he actually is a good father. My hope was that "Al" was going to be a fake name and part of the challenge was going to be tracking down different murders to find "Al".
But by all accounts Al is Al. Maybe Al will run and move his family after Prater is revealed... But then it becomes Dexter: USA or "Where in the world is Eric Stonestreet?", both of which don't fit the show we just set up which is Dexter: NYC.
Maybe Al returns to NYC to kill Dexter? But that's both not his MO and doesn't seem like a risk he would actually take.
I dunno, it's just a weird loose end. Killing him at the start of next season as an opener is the most likely result... But that wouldn't be satisfying.