In my opinion it can be only some sudden governments shift in regulations and laws to ban Bitcoin
the biggest threat to bitcoin has always been people who don't understand what a decentralized censorship resistant currency means while thinking what the government says about bitcoin matters.
This has to with government policy,all because the rate at which bitcoin has spread vastly and widely is so alarming...but most selfish interested government ain't getting what they want from this and not in full control of what there country does.
I think not been able to control what's in you country is very bad, they're the highest block to Bitcoin.