I can't help but feel a strong sense of deja vu when I compare what people say about Sanders to what people said about Obama in 2008. That's not to say that Sanders will start a wave like Obama did but I sincerely believe it's way too early to write him off. Sanders could easily project a much better image to minority voters than Clinton, given his track record with the Civil Rights movement. He was arrested at a protest against segregated schools, he was present at MLK's "I have dream" speech. That could easily be spun into the image of a pro-minority President. I also think you can't discount the endorsement he is starting to receive from people like Run The Jewels' Killer Mike.
You might be right there. If Bernie can connect with minority voters, then he can really give Clinton some trouble. I just don't think that he can win with the youth vote. The polling is much thinner in Nevada and South Carolina, so it remains to be seen if the narrative that Clinton will fair much better in those states is correct. Clinton's email issue could help Bernie too if it doesn't go away. As an aside, IMO the GOP's best chance at the Oval Office is Rubio vs. Sanders. That would be an interesting election.