Meaningful seems like a odd word to choose, as it contains the answer itself. What rule restricts our beliefs to just propositions that can be meaningful? Why, we could ask ourselves if the proposition has meaning.

The "atoms" rule seems fine, if one takes out the word "atoms" and replaces it with "state of the universe," with the understanding that "state" includes both statics and dynamics. Thus, we could imagine a world where QM was not true, and other physics held sway- and the state of that world, including its dynamics, would be noticeably different than ours.

And, like daenerys, I think the statement that "Elaine is a post-utopian" can be meaningful, and the implied expanded version of it can be concordant with reality.

[edit] I also wrote my koan answers as I was going through the post, so here's 1:

Supposing that knowledge only exists in minds, then truth judgments- that is, knowledge that a belief corresponds to reality- will only exist in heads, because it is knowledge.

The postmodernists are wrong if they seek to have material implications from this definitional argument. What makes truth judgments special compared to other judgments is that we have access to the same reality. If Sally believes that the marble is in the basket and Anne believes the marble is in the box, the straw postmodernist might claim that both have their own truth- but two beliefs do not generate two marbles. Sally and Anne will both see the marble in the same container when they go looking for it.

Again, the bare facts agree with the postmodernists- Sally and Anne would need to look to see where the marble is, which they can hardly do without their heads! But the lack of an unthinking truth oracle does not make "the concordance of beliefs with reality"- what I would submit as a short definition of truth- a useful and testable concept.

And 2:

Quite probably, as it would want to have beliefs about the potential pasts and futures, or counterfactuals, or beliefs in the minds of others.