What if instead of having to open menu select tier 1 click click click back out open menu find tier 2 item you want click click click just have "conveyor belts" and scroll wheel to the different tiers? This would work extremely well for walls foundations ramps etc where you are constantly having to switch. Check out Space Engineers. They have a block that contains all the different variations of it in one hot bar space and you just scroll to the block you want and click to place.
At the end of the day having to change your hot bar all the time is annoying and this would make it way more friendlier and easier to use.