I'd also love to make better use of the vertical space of the home screen. Compared to Nova-launcher (which I have used for a couple of years on my previous phones), having more grid options (esp. vertical) is the only thing that I truly miss in the stock launcher so far - except that, it does a very good job!
Maybe it's too difficult for the programmers to program/add a 5x6 or 5x7 grid? Or maybe simply almost nobody missed it yet?