I agree the article is just trotting out stuff everyone has seen before and doesn't seem particularly perceptive.
I think the third culture thing is possibly a red herring - the rootlessness is to do with moving often and crucially not being integrated and part of anywhere. If you live somewhere in the UK that you never felt a part of, because you have held yourself, or been held by your parents, apart from the community, you will feel absolutely rootless, without a third national culture involved. This can be within a country, although extra languages and cultures in the mix will exacerbate it if handled wrongly.
I think the "home is where your family are" idea is dangerous for children - it works when children are young enough not to want more, but once they fly "the nest" there is nowhere to go back to if parents move every few years. For adults its fine - if you as an adult decide to start a nomadic lifestyle, but a nuclear family is not a home, and if something happens to the parents the child is doubly orphaned, as the parents are their world - a very psychologically vulnerable situation potentially.
The comments are more interesting. This one though applies to me, and my parents moved a lot (including a couple of separate "locums" abroad when I was small, but otherwise it was moves within the UK:
"I don't have anywhere that I feel truly at home. I have friends all over the world and I can get along with anyone. I feel that this set of experiences will become more common and provide one with useful skills in life, especially in this global economy.
However, I'm jealous of people who know where they belong. Maybe they didn't have the chance to know two cultures or grow up speaking two languages fluently, but all the experiences I've had aren't easy to share unless its with another TCK.
In all, that means that I can only really relate to people who also have no fixed point of origen and who are as restless and unsettled as me.
I'll probably raise my kids in the same way that I was, but I'm not really convinced that it's an overall better way to grow up. It's just a fact of life that you have to deal with."
My kids are 2nd culture kids if anything, we live in a country that is not mine but is theirs and their fathers, and I have no intention of moving them around if I can help it, because I don't want them to feel rootless - I don't think it is a non issue, but it is only a problem if parents don't think things through, blithely assume "children are adaptable" and use that as an excuse not to consider the implications of moves (or anything else) for the kids, and prevent them integrating anywhere.