It's that fact that the normal sized GUI Does not fit twice the amount of inventory space especially with Armour in it too, I know he can change the GUI size but that is what that whole post was about; other ways to fit it all in. One of the idea's I would consider him looking at is that there should be like a button to flick to the other part of the inventory, easy access and easy to dump all unwanted items in it; Then maybe have bags or such that you can craft that adds more pages in your inventory.