Your right about Niall being single and has a clean late. On snl someone shouted I love you liam and the news guy said Liam was the obvious choice in 1d. Liam was everywhere after the weed video. Hq's every week and Sophia was pushed too and it felt like Liam was being pushed instead of Harry but then we couldn't compare Liam's push to nialls this last week
Okay, so the best I can find for the SNL thing is this, which is literally just a girl in the audience screaming "I love you Liam." Sorry if that's not what you're referring to. I can't find the other thing you're referring to, but I do remember when it was going around that one of the late night talk show hosts chose Liam as their favourite member of One Direction. We also know that Jimmy Fallon talks about One Direction and Harry Styles all the time.
The thing is, neither of those things look like they came from 1DHQ. I've heard the opinion that Jimmy Fallon references One Direction all the time to create buzz, get in the press, and pick up some of their fanbase. (And it seems to be working). I don't think it's at 1DHQ's request.
I actually do have an opinion on why we were seeing so much of Liam and especially of Sophia earlier this year. I think that Sophia is being groomed to take over Eleanor's role, and Sophiam will be the new loved up couple. Whether this is because Louis refuses to cooperate or as part of a coming out strategy, I don't know. I have a whole post about it here, and you can check out my Sopheanor tag.
Since I think that the yacht outing, etc. were about that shift, I don't think that the intent was to push Liam as the new frontman.
What we've seen with Niall, on the other hand, is typical Modest/HJPR strategies (the Sun, Shoreditch house, mutual promo with 5SOS) with the exact same narrative they used for Harry (heartbreaker, womaniser, mansion in LA). That makes it look like Niall is being given the same image Harry was, using the same tools. Conclusion: he's the new frontman.