Adding another area of a court proceeding that relies on "experts" is already a problem. Even when the deep fakes become good enough that they can't reliably detect them, they will continue to claim they can.
And if they wrongly testify that a genuine video is fake, it's much harder to claim that they submitted false evidence.
Yeah, if there's one thing the worldwide politics of the last several years has shown us, it is that punishment is swift and severe when governments knowingly lie to their citizens.