I agree. Something has changed.
My best guess is it is China's position. Un just visited China and seems profoundly altered. The Chinese may have told him that supporting him being crazy was too high an economic price for China to pay if it ends up with repercussions. We also know something went very wrong with NoKo's nuclear mountain test site. Again, the Chinese may have said to Un we will not allow you to pollute the neighbourhood.
I think the Trump administration can probably claim a role in changing China's attitude. Mattis sent a fleet towards NoKo and that likely got China's attention. Rex Tillerson certainly spent a lot of time over there. I don't suppose we will find out what role he played for a long time. Trump may have offered the Miami condos at a "knockdown" price as the package sweetener. ;-)
Trump will (and ought to) take the credit, of course, because he hired both Mattis and Tillerson. He may have hired Bolton and Pompeo to try the same sort of aggressive tactics with Iran. Being the bigger bully can sometimes be effective as a diplomatic/military strategy - but only with certain sorts of regimes.
Obama was clearly seen by everyone as a paper tiger. This was the risk I was always worried about. I agree with the analysis that his non-response to the Syrians breaching his red line was that Putin took Crimea and Iran was emboldened. Probably the Chinese and North Koreans saw weakness there too.
But it's far too early to get excited. NoKo has history.