As with most arguments of this nature it sounds OK-ish until it gets concrete. There is no way to scale the cost of cracking encryption to future computing capability. It's like saying "A terabyte! Consumers will never be able to store a terabyte!"

Widespread cracking of 10 year old encryption would be a security disaster, which is why cryptographers think in terms of astronomical numbers, not earthly scales.

Lastly, why, given their track record, are you willing to take US law enforcement at their word? Do they deserve that consideration? Like any potentially deadly tool, law enforcement has to be approached with caution.