I think your memory may be faulty or you weren't that well integrated into the local "scene". 5 years ago was 2013, I was already living in Berlin back then and Neuköln was already billed as "the next Kreuzberg". 10 years ago...you may have had a point.

But also remember that then and now we're only talking about very specific areas of Neuköln which are super hip, it's actually a huge district and most of it is still "not cool". The bits close to Tempelhofer Feld and Kreuzberg have been gentrifying for many years.