I think some issues are adressed to avoid overcombed multiclassing now. First of all, with apprentice levels, it is less problematic to take just one level of one class and gain many benefits. The first level now gives some benefits, but not so many as 3rd edition. Second, with ability improvement/feats tied to class and not global level, many people will want stay in one class for at least four levels. Saves do not stack anymore between classes, once they are tied to abilities. The only real issue I perceive is a fast attack bonus progress with multiclassing, assuming we just add the bonus from each class together.