I've also noticed that Dawn was created 9 months after IWRY. And we know Dawn was genetically made from Buffy, not directly from Joyce and Hank. One could say that Buffy is Dawn's real mother, not her sister, and that line was blurred even in the show sometimes.
The writers, if they were smart (they often aren't) could actually do something with that to mine an immense amount of new and sudden drama to a stale franchise. It would be interesting, at least.
Connor and Dawn as half-siblings (I will never accept anyone but Darla as Connor's mother) would be an interesting storyline. It would throw a wrench into the works of kinda 'shipping them, but the half-sibling thing seriously would be INTERESTING. It would also bring Angel quite shockingly back into both Buffy and Dawn's lives if he were actually the biological dad from a day that was never supposed to happen.
It would also make IWRY relevant as having ever happened (something Buffy likely still hasn't learned about). Angel gave up his life for Buffy's foretold death, and yet, she still died anyway. When he earned a life in The Trial, Connor was born. It seems that the PtBs royally screwed over Angel when they said that Buffy was destined to die sooner if he didn't take back the day, only for it to still happen. Playing by the PtBs' own rules, Angel is owed another life. Now, it's also possible that the reason Willow was allowed to even resurrect Buffy was because the appropriate trade of a life for a life had actually been made (it wasn't the deer sacrifice or the thaumogenesis hitchhiker). Angel's sacrifice in IWRY was for the foretold death and life of another!
Connor, even though his powers are much more directly related to specific vampire senses (hearing, sight and smell, which Slayers don't have), is pretty much the closest thing to a male Slayer, even if he's more of a dhampir (except for the fact that he's from the union of two vampires, not a vampire and a human). It also brings to mind Melaka and Harth Fray. Even the fact that Harth is an actual vampire kind of echoes in Connor being dhampir-like.
Dawn was made from a Slayer. Connor was made from vampires. Like Buffy and Angel, they're two things that are exact opposites. Their real biological 'parents' are a Slayer and vampire who were forbidden lovers meant to be enemies because of what they are and actually brought together by Higher Powers in a way that wasn't an accident and prophetic. Buffy and Angel, unlike Spike, are always at the mercy of prophecy and destiny. Dawn and Connor are also steeped in being tools of prophecy and destiny. That they survived as their own individual selves past being the Key between dimensions and a tool to bring about Jasmine's Utopia is purely accident.
Dawn desperately needs a real arc about what she is beyond Glory's use of her as a Key years ago. Connor's arc and destiny had juice beyond one season. The fact that he's a superbeing and took a long time to develop into a healthy state of mind kept him useful from a writing perspective and allowed him to be part of the superhero action. Dawn ended up just being there and feeling decidedly not useful (to the point where Potential largely was about just that). Dawn's Key-ness should have more to it.
God bless you! God bless everyone in your life!