I've actually wondered how parents are going to play into the story later. Here's a run down of my expectations:
-We should expect to see Usopp and Franky meeting their fathers as both are well known pirates.
-Nami was separated from her parents during a horrible war involving the WG that occurred shortly after the start of the Age of Pirates. This would fit the timeline of when Dragon may have begun his revolution, so it is possible that nami will meet a parent involved with the revolutionaries or that had been captured by the WG (Vegapunk?)
-Robin's father may or may not be Gol D. Roger, and thus her parentage could play in at some point as well.
-Luffy's father will be important, obviously. However, I'm really hoping that they meet his mother at some point as well. Of course, this goes to my other speculation that Luffy's mother is another daughter of Roger, and would thus be a powerful woman with a round face and small pointy nose (see? she could be robin's half sister…)
-Sanji and Zoro have no known back story involving blood relatives. Both seem to have left their families to follow their dreams at very young ages. It seems unlikely that their families will come into the story.
While I would like some of these parents to become minor figures in later arcs, I'm very glad OP hasn't fallen into the same trap as Naruto, where everyone has parents who are just stronger versions of themselves. That just made me wonder why the story follows the loser children instead of the more interesting parents.