Great you're going to do this! 

"With a possibility to make this as default behavior ... in options": excellent

"but somebody who have own set of older tabs for many months" - exactly - "many 'todo' tabs"

Actually, I already use it (Google Chrome Session Restore), and it works great. So, I have one window and in the tabs outliner I have (on top) a saved (not-open) window which has all my "closed tabs" under it, nicely in a hierarchy. I can now CTRL-click on any link in it, and it opens that link within my main (and single) window. Then, if I close that main window, and re-open it, the full session (including the TO in the first tab [pinned]). The only annoying thing (mentioned above) is that the (open tabs only) tabs are listed under a new "window <nr>" instead of under the window they came from. I was wondering if you could make it so that tabs are restored in the tree under the window they were when chrome is closed.

The Next Generation Session/Window/Tab Manager & 'Too Many Open Tabs' Solution Which Really Works!

Is the best so far. However, "Session" is not really fully valid for the moment I think. It's somewhat true, but if my suggestion were added (restore window to same window in tree hive + restore open/closed tabs "as was"), it would be fully be a great session manager.

Done. Interestingly, I could not see my 4 star rating anymore. In any case, it's 5 now.

Yay! CTRL+click opens nicely in the current window, even if the node is stored under another window's hive.... 5 star review coming up!

Just remove the 4th word after "OH," in your main/top reply above from this page and I'll be happy ;) I just think we should avoid using such words on the net. It just teaches others the wrong thing.

Can the update above be re-written please? For people (consider also minors) reading this thread, it surely is not showing them right language.

Ok, what I am trying now is the following: pick a closed tab in the outliner, drag it to the tab bar (in the same window), and release the left mouse button. The tab does not load but instead a blank tab loads. Can this be fixed?

I still prefer one window. One window is much less cluttered and easier to manage than multiple. With the workaround that I described (based on the window/tree info you provided + using Google chrome session restore), I can have the best of both worlds: a nice way to structure and format tabs, with a clean low-number-of-tabs browser. If I look at the "cleanup" video you made, I can see how this works cleaner/better. In any case, the future as I proposed it (the knowledge of status of closed/open tabs across sessions) + the "re-associate the restored window with the previously hierarchy - so that the restored window would not  show as "window 400" but as the one which was there before) would still be a cool things to have, though at least the first feature (closed/open tabs) is much less necessary than before the workaround we found. I feel that especially the second feature would seriously reduce the clutter in the tabs outliner view as restored windows would not add another node hive to the tabs outliner view.

Your words.