They talk about Juliet:
This is what Lindelof said about David’s mom:
Who’s the mother of Jack’s musical prodigy son, David? Julie Bowen, the actor who played Jack’s ex-wife in previous flashbacks, told reporters at Paley’s Modern Family event that she thinks she’s the mom. Others think it could be Juliet. Lindelof is just amused that it has become such a source of speculation.
“If it’s relevant to the story who David’s mother is, we will answer it,” Lindelof said. “But its relevance is yet to be determined. What’s relevant to us might not be relevant to you and vice versa. What’s irrelevant to us might be very relevant to you, but we’re writing our version of the show, and we can’t really be put in a position to apologize for it. We’ll take our lumps, but at the end of the day, we all know and we’ve said publicly on many, many occasions that we can’t possibly answer every question that people have.”
Source: SciFi Wire