You could have one Bayesian network to show how likely Mormonism is, and a separate one for how likely it is for a holy book to say that otherwise. Alternately, you could just give the ratio of how likely it is if Mormonism is true and how likely it is to be stated otherwise. I suppose you'd have to calculate for a given religion, and then multiply by the number of religions.
Well really, that would be far to general. If we're questing for the One True Religion - or, rather, the One True Belief System, with atheism included in there as a belief in the Merely Real - then we'd need separate Bayesian networks for each religion. Otherwise one of the less wacky religions would have its score brought down by one of the more wacky ones, when in fact they exist independently of one another.
Sounds like a daunting project. Shall we get started? :P
In this comment thread, I gave the following idea, on the topic of a method by which one might judge the Book of Mormon from a rationalist perspective:
I would appreciate feedback on this idea, for an admittedly selfish reason: I am trying to instigate in myself a Crisis of Faith. So, here are the questions I pose to you: