I work with multiple monitors and often want to pull out a pinned tab to a new window (without losing its pinned status) to fullscreen on my other monitor. Currently the best way to do that is to duplicate the tab and then drag it out of the tab bar. It doesn't make much sense to me for anyone to ever want two duplicate tabs next to each other in the tab bar though.
I propose fixing this as follows:
OR
OR
Another idea could be to offer a "Pop out" function, since that's what I'm really after. A popped-out tab would suspend in the other window and the pop-up window would be displayed with only a title bar and no browser chrome.