I want to start off by saying Mate has possibly the best tiling support I've used on a non tiling wm. However, I recently noticed there is no option to tile vertically.
On a normal wide screen monitor this feature would be pretty useless, however, with a vertically rotated monitor, it's surprisingly important.
I can see how this would be a low priority enhancement, since vertical monitors are rare. But if someone was able to point me to the area of code that handles the current tiling, I have a guess that it shouldn't be too hard for me to adapt in this feature if there is interest.