The formula in question is of course too easy, at least as far as the older idea goes. For the sensus fidelium has always been that baptized infants who die are indeed saved, with the required faith and devotion being supplied vicariously by those members of the Church responsible for the baptism. Yet that very fact points up the authenticity of the later development.
It must be admitted that, although we are bound by the sacraments, God is not. That is to say, while as members of the Mystical Body we are obligated to have recourse the sacraments when appropriate and are culpable when we don't, God's salvific grace is not limited to the formal sacraments any more than to the visible Church herself. Just as, in the case of baptism, that faith which the recipient cannot supply for himself can be and typically is supplied by the confessing and baptizing Church, so too can faith which does not entail explicit submission to or even knowledge of the Church be elicited by God through means not prescribed within the Church. While the visible Church remains the normative sign and instrument of Christ's presence in the world, and thus the necessary "sacrament of salvation and unity" for the entire human race, Christ's presence and action in the world are not limited to the visible Church even as, by divine decree, they depend on her. And so even though EENS remains true, the means of attaining membership in the Mystical Body, which subsists in the Catholic Church, are wider than we can know.
That development opens up a way to apply reasoning by the analogy of faith to the limbo question. It has long been held, rightly and infallibly, that how we have chosen in life when we die determines our fate for eternity. But in the case of baptized infants, their salvation is assured if they die before being able to make choices. Now those incapable of choice cannot love, and therefore cannot love even God; yet God is love, and those who die in his grace partake of his nature; so some sort of growth into choice must be available to those who enter heaven without having been able to choose in this life. If that's true of baptized infants who die, why could it not be true of unbaptized infants who die? If the former attain salvation by the vicarious faith of the Church, why couldn't the latter? Of course such an outcome is not guaranteed for the latter; I suppose it depends on who's praying. But we can surely entertain its possibility if we drop two old ideas: the Augustinian nostrum that original sin is personal guilt—which the Magisterium, expressing itself through the CCC, has done (cf. §404-405)—and the long-popular, epicyclical alternative that a state of purely natural happiness is in store for infants who die unbaptized.
As Al Kimel's articles suggest, such is what seems to be going on in the Church right now. It is authentic development of doctrine. It is not mere innovation, for similar ideas have long been held among Eastern Christians; neither does it negate anything taught infallibly by extraordinary or ordinary magisterium. It's the flowering you get after a needed pruning.