> There's a digital currency in our future, but I guarantee that it won't be decentralized and that the government will have the signing keys.
That might be possible, but its too early to say anything at this point in time. The thing is that Bitcoin has technologically established itself as a stable crypto-currency and also an open-source wallet software. In future, some governments may also come up with their own centralized digital currency, but it will be too little and too late compared to something like bitcoin or litecoin.
Besides, bitcoin is international and a lot of people have started transacting in it already. Now, the government has to tread carefully about this, despite all the talk of sovereign nation and government upholding its economic control, no government can go against its own people in this day and age.
Also, actually persecuting the public for using crypto-currencies is against their own interest as it will create something like a Streisand effect. Right now, only the technically inclined know about bitcoins, blockchains and wallets, the rest treat it like some magical buzzwords. But if they start persecuting, a lot of other non-technical folks will also come to know about it and they will also start using it.
In short, the future depends on the mood of the people of the nation and not the governments. Its a fallacy that money begets is value as a legal tender by the government. Rather, it gets is value because its "generally acceptable", in other words the people accept it. People of a nation are above the government, not the other way round.