The further the series progresses, the more I think that this idea (great as it sounds) is mostly fanon. The time they spent together in part one was so brief and so far away now, and if you really think about it, not all of it was very functional either. The bulk of their relationship has been dominated by conflict and pain. They care about each other (well, Naruto and Sakura do), but even if everyone are united in the end and blah blah blah, we have little concrete evidence to believe the situation would pan out the way OT3 fandom likes it.