Well no, thanks. Thats actually something basically completely different then what i suggested.

I would rather see more without the need to click anything to get it.
And it seems to me that seeing two rows in the hotbar would be a good compromise. It would also make it easier to click just once to bring up the third row - in the same way its done now. Only you would always have two rows visible - because thats just better then one. Easier, more functional, and more elegant.