Right now in ksp there is 3 tiers which sounds good. I feel like there is really 2 tiers though. If you think about it .5 meter parts are just too small for any good use in rockets, they are for satellites probes and other small things. Im not saying that they make a good upper stage but there really needs to be a "real" 4th tier like 4 meter parts. Another Problem i frequently have with just 2 "real" tiers is that i can only put multiple rocket engines on 2 meter parts. You might not understand what i mean but ill explain. Lets say i have some LV-T45's, to make rockets look cooler and better i would get a 2 meter parts and put 3,4,5 or more underneath it. Its nice because you don't need mods and its just cool looking. It also helps if you don't have mainsails in career mode yet. Now if there was a step up like 4 meter parts now i can put 4 skippers on one and a mainsail in the middle, its like i have my own Saturn V without addons. Also another reason this would be useful is because of the booster issue. KSP at the moment has its own thing with flying. Instead of building more vertical stages people build horizontally with boosters. This is unrealistic and one of the reasons why it has to happen is because of how there are only 2 "real" sizes. If there were 2 then i could put MK1-2 command pod on top with some 2 meter parts then the main booster could be a 4 meter one. I really hope this is looked into for the sake of realism and just better gameplay, i know i could just download kw rocketry but i want to play legit kerbal space program, not with mods.