Regulators really only get involved in allowing/prohibiting innovations very late in the game. I'm thinking of how Air BNB and Uber were allowed to grow really huge despite being blatantly in violation of a lot of laws in a lot of places (for example restrictions around subletting in contracts between tenants and landlords, regulations around running businesses that are hotels or taxis, etc). Only after they had gotten really big did regulators start to think about whether or not they like what's going on, and then they shut down large parts of the sharing economy.
For bitcoin there are only two scenarios in my mind: Either it dies right now for the problems it is facing right now (network externalities around lack of merchants/customers outside darknet/illegal stuff, volatility etc), or it overcomes those problems, gets really big, and is then killed by regulators.
For the most part the trend in regulation of financial services and financial reporting has been: erosion of banking secrecy (even Switzerland and tax havens in the Carribean are now sharing data with law enforcement), anti-money laundering regulation tightened (FATCA/CRS), increased requirements around creating transparency about ownership of legal entities in cross-border corporate structures (e.g. "persons of significant control" register introduced in the U.K. and many European countries), increased reporting obligations around cash transactions even for small businesses (parts of Europe are now mandating the introduction of electronic cash-registers capable of reporting on a transaction-by-transaction basis even for small businesses like a self-employed taxi driver), etc. etc.
Allowing bitcoin to happen would not fit into that regulatory trend AT ALL.
It's just that bitcoin isn't big enough yet for regulators to even be thinking about it. But it'll happen.