My efforts to connect with the Bertelsmann Foundation have not proven fruitful just yet. The two people I contacted are very busy and did not seem open to chat. I can totally understand that. They are currently preparing the 2019 SDG Index report and have a lot going.
But I stumbled upon a (German) paper by the Bertelsmann Foundation on SDG metrics for German cities. I’ll read through that and see if it gives me some new Bertelsmann Foundation members to connect with (its authors, for example).