if we got what looked like a working Theory of Everything that implied that the universe is infinite, you'd probably assign a non-zero probability to the universe being infinite.

The hypothesis that the universe is infinite is equivalent to the hypothesis that no matter how far you travel (in a straight line through space), you can be infinitely certain that it won't take you someplace you've been. Convincing you that the universe is infinite should be roughly as hard as convincing you that there's zero probability that the universe is infinite, because they're both claims of infinite certainty in something. (I think.)

I'd like to be able to boil that down to "infinite claims require infinite evidence", but it seems to be not quite true.