You have lot more faith in central bankers than me. They're only in control until they aren't. They claim they're not concerned about bitcoin and alt currencies. Yeah right.
I don't have any special insight into what the fed thinks but I'd be surprised if they were concerned about cryptos. If they ever became a plausible threat to the dollar they'd simply be legislated out of existence. If you can't buy and sell something, it tends to lose its value.
But personally, I don't see any crypto becoming such a threat. They're all far to cumbersome for everyday use. Plus there's always the risk of theft through hacking. If you have to keep all of your coinage in off-line wallets to ensure security, that tends to make them difficult to use.
And even if you do manage to find a solution that let's you carry a crypto around with you in a secure device, there's still the issue of volatility. Why would you ever hold something that you know can rise or drop in value by 10, 20% or more in a matter of hours.
If you actually needed a crypto for a particular purpose, it would make much more sense to just buy as much as you need when you need it.