While an interesting idea in theory... and I mean that!... in practice that's saying they just shouldn't provide answers. Even saying for the sake of argument that Google could assemble a meaningful and correct probability distribution, itself a rather bold statement, the average Google user won't know how to correctly interpret such a thing.

And realistically, asking for probability distributions over unbounded sample spaces is trouble even for human experts. I suppose the space for "are mermaids real?" is workable (there are caveats like "yes but extinct", but yes/no is basically sufficient), but for anything subjective or political it's almost hopeless.

That said, this is a really interesting idea for behind-the-scenes work. The public might not want percentages, but I suspect experts could get some interesting results by diving into confidence levels and secondary answers.

But google isn't even making a truth claim. Google fundamentally doesn't understand the claim, or how to grade it. All the google engine knows is the statistical properties of words and phrases involved and associated with the claim.