Neat, and works well for the toy example with 4 tabs open. I don't really think it would work as well for the "tab collectors" as they think. They seem to be aware of this too, since none of the screenshots in the post have anywhere near what I would consider a significant amount of tabs open. I use the tree style tab extension on Firefox[0], which I cannot live without. Horizontal tabs become useless after about 15…
However, it quickly becomes tedious to open the set of windows (with relative tabs) and software need for a certain task/project (shameless plug #1, see this previous thread https://news.ycombinator.com/item?id=21995823).
To at least avoid closing windows, but not to have my desktop cluttered, I minimize them (on a Mac), but then I find it difficult to reopen the exact window I might need. To mitigate this issue I (shameless plug #2) did a small app that shows a big cover so that it is easy to find the window when minimized. It still is under development, so lots of bugs and few features. If you want to give comments, its https://cver.vernizzis.it/ :-)