I mentioned this earlier but 2 rather unpredictable events could put a nail into bitcoin's coffin:
1. There would be a terrorist cell discovered in US ground who got their funding via bitcoin. Congress would outlaw virtual currencies overnight, not to mention bitcoin is already breaking 2 existing US laws, just nobody is enforcing them yet:
a/ Thou shall not make a competing currency to the almighty dollar.
b/ Thou shall not operate a money transferring business without special permission.
2. A large retailer (Walmart, Amazon) introduces its own coin, that is even an improvement over bitcoin, but in every other detail it is similar (minable) and right from start has 10-100 million users. Amazon could donate 1 coin to each of its users (100+ millions) and even if only 10% using it (unused coins would go back to Amazon) that is 10 million user. Bitcoin after 6 years still doesn't have a million users.
Going back to point #1, it could also be a famous blackmailing case or kidnapping where the criminals use bitcoins. That is all it takes to drop the price into double digits....
My 2016 range prediction is 200-680. I am not saying we will go up to almost 700 for sure, but if the rally continue, I don't expect a new ATH like 1200$....