In Shariah, there is no valid reason to accept Bitcoin or other Cryptocurrencies as a currency. It is just an imaginary number, which is generated through a complex mathematical process. It is purchased for Gambling or Speculations, and used in illegal or unlawful transactions”.
I don't suppose that your comment means that Bitcoin is probably Haram based on the argument you are putting forward but you do understand that, all the ills you mentioned about the possible use of Bitcoin are also true for Fiat money? except for being an imaginary entity. so do we say that Fiat money might also be haram? I think it is what you do with you Bitcoin that matters.
The only thing that puts BTC into 'cautious' category is No government has accepted it as legal tender. Once Governmens start to accept it as legal tender or even as asset, it will become clear cut halal.