Shell worlds

What this article describes is not a shellworld. What it describes is worldhousing, which is not a new idea. Now I happen to find worldhousing in some ways superior to regular terraforming, because you don't need to pile up atmosphere until gravity packs it down to something breathable, and you don't have to roof over the whole world at one time. You can start in one place and expand over time, or start in several places and let them grow together. With regular terraforming, you either do the whole planet at once or you don't. It still lacks a lot of the advantages of O"Neill habitats, but it has all or most of the advantages of regular terraforming, and others besides.
This is a shellworld:
http://www.orionsarm.com/eg-article/47856a978e732
It's not a new idea either, and that's not what this article is describing.