It was a very encouraging and positive moment. Diess clearly recognizes that the future is electric and that the best path is to transition as quickly as possible. He is trying to pull that most difficult of magic tricks -- convincing all of his shareholders, directors, employees, suppliers and customers that despite the short term pain it is better to welcome the future and move quickly.
I'll show my age but Diess embracing Elon and Tesla reminds me of the 1970s/1980s when Toyota and Honda embarrassed US car manufacturers with vastly better quality. In response to the shock (and hit to the bottom line) US manufacturing companies embraced Deming and 3-sigma manufacturing (precurser to 6-sigma). That didn't mean they would partner with Toyota (although GM did in a small way) but that they recognized that the world had changed and that they had to make fundamental changes in how they went about their business, because sticking to the status quo would be a disaster.
Bottom line: I don't think Diess' positive comments about Elon and Tesla means VW and Tesla will do business together (although it's possible that could happen in a small way), but rather that Diess wants VW and all of its stakeholders to embrace Elon's vision and move as swiftly as possible toward EVs. It's no different than a 1970s/1980s auto exec acknowledging that Toyota and Honda were doing some things right, and signaling that it was time to follow that path rather than stick to the old ways.
Either way it seems like a strong positive for Tesla and the mission of accelerating the transition to sustainable transportation. I really enjoyed watching it.