I think some of you are obsessing over this purity test with his party label when it doesn't really matter. Personally, I think it's actually an asset:
A growing number of people can relate to his decision to stay independent. Dems need left-leaning independents -- excluding left-leaning independents from the process will only hurt dems. Dems embrace Sanders, left-leaning independents feel like they're part of the big tent -- feel listened to. Doesn't matter who's registered as a dem, what matters is votes and results. This obsession over party labels just feels like petty partisan nonsense to a lot of people. And if you really want to get Sanders and other left-leaning independents to adopt the dem label, you'll need to evolve the party to fit them. Personally I kind of lean toward a coalition approach -- don't worry about the labels so much.
Sanders seems to be doing this stuff on his own -- afaik, it's not the party setting up these TV debates, so who's putting him on a plane above the rest? Nothing stopping others from doing the same and I've already said I want to see more people doing it. I'm not as anxious about disagreements between Sanders and mainstream dems -- I think there's room for it in a larger coalition and it can actually be healthy.