Xfce is sticking with gtk2, in order to avoid the some of the v3 issues discussed here.
Individual applications may still switch to gtk3, in which case those applications will experience the breakages. But that can't be helped-- it's up to the individual application developer. In the same way, you can fire up a KDE application in Xfce and stumble across various KDE bugs.
I have no idea what will happen in the long term with regard to Xfce and gtk. Last I checked, there were no developers working on any version of gtk full-time anywhere. So maybe it would be practical for Xfce to fork gtk 2.x. Or maybe gtk 3 will settle down and they'll switch. We'll see.
P.S. I use Xfce myself. I think it's the best desktop out there today for Linux.