I didn't see the press conference "live" in which Mette-Marit cried and spilled all the beans, nor have I seen it in its entirity, though I have seen clips here and there.
My personal impression of things, if I were Norwegian, I would appreciate more my future Queen being up front and honest about her past than trying to hide it with the curtain of "it was all in the past." All the things that Mette-Marit did in her life before Haakon, sordid or not, out of wedlock child and all, lead her on the path to meeting Haakon. And really, her past was not all that sordid -- maybe not "perfect" princess and future queen material, but it's not like Mette-Marit was a murderer or something like that.
And if she hadn't been up front and honest about her past, the partying and the drugs, et. al., then we would have a case like Mabel Wisse Smit, whom had a relationship eons ago with a gentleman associated with organized crime and wasn't completely up front about it because it truly was in the past. Yes, Mabel will not be queen one day, but she still had a past that needed to be fessed up to.