If Sennheiser referred to the HD 800 as their "open back" flagship and the HD 820 as their "closed back" flagship, what could you infer about the product positioning? Which one does Sennheiser think is better? Seems like you could partially look at the product code (820 > 800). You could partially look at the price (HD 820 more expensive than HD 800), and so on. Not to mention, the HE 1060 is technically Sennheiser's current "open flagship". What does that say about Sennheiser's opinion of the HD 820, if they can say it occupies a flagship role alongside their HE 1060! Wow! Huge endorsement. (Sarcasm alert)
If we are pulling poorly translated quotes out of interviews, I think you've lost the plot. What does it matter what the "successor" relationship is? If you like how the HD 820 sounds, and it sounds better to you than the HD 800, you should buy it. If you prefer the sound of the HD 800, buy that. It's really quite simple. All that really matters is that the HD 820 and the HD 800 sound different, Sennheiser has brought a new option to the marketplace, and it's up to you to evaluate whether you like it or not. Philosophical pontificating about successor relationships seems to be entirely beside the point. If you would sleep better at night knowing the HD 820 is not a successor to the HD 800, I think the Sennheiser marketing department would be totally OK with that if indeed that allows you to get better sleep.
Getting back to impressions, it seems the HD 820 are getting almost universal praise from the early initial responses around the web. Good bass extension, extremely clear and transparent. Besting an open design with a closed form factor - leave it up to Sennheiser to pull it off. Can't wait to hear them.