When we begin paying our taxes out of BTC, that is the moment when it had become 'the next big thing'
Not really. Who on earth will use his precious coins to pay their by-government-created debt? And if I remember correctly, there is already a country where you can use Bitcoin to pay your due taxes up to a certain amount. If we go by your logic, it means that Bitcoin has been 'the next big thing' for quite some time already. Aside from all this, Bitcoin is already in progress to become the next best thing, and that's by people utilizing Bitcoin's technical aspects (e.g. currency aspect, store of value aspect, voting and proof of identity purposes, etc). The more people utilize Bitcoin, the more valuable it becomes, it's that simple.
Nice said. The idea behind is simple, the demand and its reaction by the market. If more demands creates which is now happenning, the price goes even faster. For the adoption, we need more people in bitcoin so that more people use it. And it won't replace fiat.