Even 5 years ago when I spent 3 months in Berlin the idea of calling Neuköln trendy would have seemed pretty nuts. So I think that suggests something radical is happening.
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.
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.