If A believes h is incoherent, but B is unable to demonstrate h's incoherence, A should regard B's inability to coherently explain h's incoherence as evidence that h is not , in fact, incoherent.

Er, 'A' believes 'h' is coherent in this case.

I have realized, though that my statement was profoundly unclear, even after the edit.

Let me attempt to rephrase yet again, more precisely:

"If a bunch of people on LW tell you your hypothesis is incoherent and you need to dissolve your question, this should not be considered evidence that your hypothesis is sound, merely because nobody directly refuted your incoherence, in terms currently comprehensible by you."

Or, by analogy, if you go to a biology forum and ask about missing links or why there are still apes, and then when you get explanations that dissolve the wrong questions involved, you say, "aha, but you still haven't answered my [wrong] question, so therefore I'm right", this is not sound argument.

The denial that B's failure to coherently explain h's incoherence increases the probability that h is coherent expresses the common failure to regard others' beliefs as evidence of what's true.

In this case, though, the incoherence has actually been quite clearly counterargued by many, and is already thoroughly refuted by the sequences.