Really shouldn't be posting about the mechinical design of Minecraft for an hour's explaination worth of reasons, but I will say that I hate how often people say that more slots in the inventory would do anything to help with the inventory problem. The issue is in the disparity between maximum item capacity and the bottleneck in variety, adding more slots makes this worse. It's like adding lanes to congested road. The solution to the problem is in more variety compressing mechnics, such as the bundle. Some have suggested some blockshape system that would allow slabs, stairs and what-have-you to be placed from the full block, which would probably help, but has the chance to be very cumbersome. My favourite solution is to reduce the standard stack size from 64 to at most 16, but it's a bit devil's advocate.