What if they made a "Upgrade Kit" for the Mawkrusha that would give you covers for the feet holes and some plastic basing bits to make the Megaboss easier to run on foot. They could even add some kind of platform so you could add a Warchanter or Weirdnob.
Also unrelated question, can you stack multiple Waagh!s from a single MegaBoss if you have the comand points for it?