People who claim BTC is the next mainstream currency are delusional. Its an investment commodity right now, and its way too volatile, way too little regulated and capped too low to be a serious currency contender. Seriously, the real world does not work that way, and thats not necessarily a bad thing. This goes especially for the whole decentralized and uncontrolled/unregulated part - I see it as bad thing, a lot of the regulations are in place to avoid anarchy and protect the consumers (admittedly there are also regulations that totally screw the consumer in some cases).
Right, and the problem (too much speculation, not enough actual economic liquidity) isn't even just a quirk of human behavior: Deflation is baked into the design.
Even assuming it were trivially easy and perfectly safe to use, there are numerous other risks currently associated with it.
Just look at its recent volatility, for example.