At first, I didn't think it would be successful. Purely because I feel like the majority don't know what they're getting themselves into. Because it wasn't easy like it is today, and with our current culture. The moment things aren't handed to them, they'll bitch to blizzard.
However with more thought, and with how much they've fucked up live. I wouldn't be surprised if six months from now, classic has more active users than live. They've taken everything from the game that kept it exciting.
I truly hope that this takes off, and that its better than nostalrius ever was.