While I haven’t really seen such a thing, it doesn’t surprise at all, since in some circles the idea of having any correspondence between boys and girls is considered the worst thing ever. So of course, that would include this. I think for people that have been brought up that way, it may be problematic since they would have no idea how to act, or interact, with the opposite sex, which can result pretty badly. But for people that have been brought being used to corresponding with both boys and girls, having a shabbos meal with each other would be considered perfectly normal, and a wonderful thing.
But even for people of the former group, perhaps they should have such arrangements at meals anyway, so they will become better at properly acting and interacting with the opposite sex, which is something they’ll have to do anyway when they begin dating, and more importantly, when they have a spouse.