There was a VERY STARK difference between the Catalan countryside and the urban self-governing cities of the coast. Barcelona, Girona and Tortosa were worlds on their own, where I can imagine calvinism or lutheranism (or the local flavour, let's call it Galesianism for Pere Galès, prominent Church reformer and university professor of Classics in the 16th century.) taking hold; but not in the interior... at least, not easily.
Had Aragon kept on as an independent kingdom, I can envision one of its kings turning Protestant just to be a part of the "not-France" team.