the problem with ghosting, ESPECIALLY as a tank is that you cannot creep block, or unitcollsion people into walls/trap them/bodyblock/force targeted skill shots to target you, or force attack move commands to attack you (there is fun tricks you can do with annie and tibbers while ghosted, since tibbers is not ghosted).
There are several champions whom ignore unit collision already, cho does not be concerned about creep block because one E clears the entire wave, you aren't weaving AA's properly while moving is all.
Super massive champions DO push minions aside (but only while the minions are "walking") more than their small forms, a few very small champions have very large unit collision boxes and some VERY large champions have incredibly tiny ones(alistar), this is more true of melee champions than ranged champions who have rather large collision boxes (excluding "old" champions from when league was first released, except taric and poppy).
Fizz is permanetly ghosted and takes almost no damage from minions due to his passive, this disables him from doing a large majority of things in game, but allows him to attack lead and trap people inside minion waves no problem.
Cho'gath's collision with minions is part of what keeps him balanced despite his kit's enormous power.