NSA Engineer: Hey boss, this one's using a 256 bit key.
NSA Manager: Connect it to the quantum computer that doesn't "exist".
Five minutes later..
NSA Engineer: We now have access.
NSA Manager: Connect it to the quantum computer that doesn't "exist".
Five minutes later..
NSA Engineer: We now have access.
considering that there already theoretical attacks that (marginally) faster than brute force on classic computers who knows how much more one could squeeze out with quantum algorithms.
Of course those are fairly speculative concerns.
But in AES? that sounds unlikely and really unfortunate.
I think it's more likely that large quantum computers would aid in mathmatical exploration that uncovers currently unknown vulnerabilities that could be exploited by classical systems.