Zu, think dynamic list view. You select a folder, then another column pops up, and so on until you select the file you want.
If it were to have happened I'm pretty sure it would have been done. My limited knowledge indicates that you essentially would have to create a new inline (for lack of a better term)browser control for each column. This would most likely balloon Explorer into some obscene range depending on the contents of each column.
The reason tabs are fairly functional like in QTTabbar(again from my limited perspective) is that you just use the standard explorer box and the tabs are simply controls that load that folder into the one control.