There is no way to know for sure whether this trend will continue. We are not even completely sure why previously cohabiting couples have higher divorce rates when they do marry. Therefore, we cannot know whether the trend will continue. My own speculation is that the trend will not continue.
To come to this conclusion, I first determine why I think the higher rates of divorce occur in this group. I would argue that, in the past, cohabitation was something that people did if they were not sure they were ready for marriage. In other words, it was engaged in by the people who were most likely to make unstable couples. These couples were willing to take on the stigma (which existed more in the past) of cohabiting because they were not ready to commit.
I would then argue that times are changing. Cohabitation no longer carries a stigma. It is no longer seen as something aberrant. Therefore, more people will engage in it not because they are afraid to commit, but because it is more convenient for them. It allows them the joys of living together even as they plan their weddings or get enough money to have a wedding. What this means is that even people who will make stable couples will cohabit. It will not be a behavior engaged in only by those who see themselves as outsiders in society. Therefore, the rates of divorce among such people should, I think, decline towards the same levels as those who do not cohabit.