The Pope, speaking on the subject of annulments, has recently reminded the Roman Rota that no one has a right to marriage. Meaning, apparently, that priests shouldn't just agree to marry every couple that walks in asking for a church wedding. To some extent I agree; if a couple comes to a parish and the priest thinks “this is a trainwreck, this is clearly never going to work”…he doesn’t have to marry these people, and probably shouldn’t. If I were a priest and a just-18 boy and girl showed up at my office asking to be married, I’d probably say, “Come back in 4-6 years.” This makes total pastoral sense. I’d be negligent to do otherwise.
Then again, do we really expect people to abstain from sex for that long? Well, I've already laid out most of my thoughts on dealing with the questions of marriage, divorce, and annulment in the Church in these two posts that address the issue relative to the Eastern practice. I summarized them again and elaborated a little in a comment I made on another blog:
Might it be possible to change the canons so that two Catholics who get married by a justice of the peace are validly naturally married, even if not bound in that case by the indissoluble Sacrament? Might not my 18-year-olds contract a merely natural marriage and have licit sex that way, start their family, but still have an "escape clause" (since the dissolution of natural marriage is possible, though unideal), and then seek the absolutely indissoluble Sacrament later when it was more clear their relationship was going to last?
I know there is a theological position that says, “No, the marriage between two Christians is either the Sacrament, or it is nothing, merely ‘putative’ marriage.” But I wonder whether this is really dogma, or just a theological opinion based on the way Canon Law has worked in the West for so long. Ott considers it sententia certa (ie, an opinion theologians believe follows implicitly from dogmas) but I don't exactly see which other dogmas about marriage imply this necessarily, and in any case the Church has not definitively spoken on the question.
Now, two Catholics deliberately seeking out such a "merely" natural as opposed to Sacramental marriage might still, in itself, be considered sinful…but, at the same time, it would at least still be recognized as a natural marriage as opposed to merely “putative." Meaning in practice: the children would be legitimate (without needing the special canonical exemption they added for children of “putative” marriages), and their sex would be recognized as not sinful. Except in extreme cases like incest or where it turns out two people were of the same sex...the concept of a "putative" marriage is a rather bizarre and inelegant canonical animal.
There would probably also then exist the concept that such a Catholic couple is morally obligated to convalidate the natural marriage into the full Sacrament eventually. Still, after they confessed the initial sin of contracting a natural marriage without the Sacrament, they would then have some time to fulfill the requirement to get it "Sacrament-ized." The obligation would be a "soon enough" sort of thing, like getting a baby baptized after birth, but in the meantime they wouldn't be considered to be fornicating. Because it would still be a valid natural marriage, they wouldn't be "living in sin."
Now, if the obligation to make it a Sacrament was neglected too long, this neglect could become a sin too. But how long is "too long" a delay could be subject to (lenient) pastoral interpretation according to need. If a pastor or bishop thought the marriage was not likely to last, then making it the full Sacrament right away might not be the best idea, and he might permit them to wait longer (though, on account of the natural marriage, they wouldn't be morally obligated to cease normal marital intercourse either). "In the meantime" could last quite some time...
And if this natural marriage did break up before being made into the Sacrament, then at least there is no need for annulments or anything, seeing as natural marriages are dissoluble in theory (though it's still a tragic thing and subsequent marriage ceremonies might take on some sort of "penitential" elements, like in the East).
The Sacrament would be recognized as coming only from the church ceremony. The marriages between Protestants would then not be recognized by canon law as the Sacrament (but merely natural marriages) and, as always, some marriages that did take place within the church ritual might still be found later (ie, the concept of annulment) to have not reached the level of the full Sacrament. But they would nevertheless still be seen as true natural marriages as opposed to “nothing” or merely “apparent” or "putative" marriages.