I would say that bitcoin pose no real danger to the financial system. In my opinion the bitcoin as the alternative to the financial system just gives the idea about how many people are discontented with the fiat status quo. Ofcourse showing discontency is in itself destabilising for the system that is based on the faith - fiat
There is a small additional threat to the fiat financial system. There is a disconnection of real money (of bitcoiners) from the system, that before the existance of bitcoin had provided the liquidity on the markets. That can pose additional destabilisation to the system that need to print more fake money to compensate for the loss of liquidity of money leaving the system
In fact, it works exactly the other way around
And it is a real danger to the financial system based on fiat that Bitcoin threatens it with. More specifically, Bitcoin (if it is set to expand, of course) would be crowding out fiat (whatever local currency is used in the area which gets infested with Bitcoin), i.e. more, say, dollars would be chasing less goods (because Bitcoin will be used where the dollar has been the king before), and then the "system" would have to unprint more money, i.e. diminish money supply, not expand it. That's how things are going to stand in real life if Bitcoin starts to seriously compete with fiat currencies
