If that monster ever reach combat units, what it would be used for? My guess is as movable artilery point, following frendly panzers several hundred meters from behind, being able to sucesfully destroy enemy tanks from two miles distance. So Maus does not really need 70-mm canon but longer barrel supported on IS-style manlet. Also it's worst enemies would be tank-hunting planes, so smoke launchers and aditional AA turret would be nice. So questions are now: should a battle ship-sized tank have similar style camuflage scheme as ships? Would this size of vehicle still had tools hanged from outside?

The purpose of the 75mm was to throw HE and HEAT quickly. The 128mm was a two part (projectile and charge) system and that slowed down fire considerably.

Adding a AA capabel turret, based on one of the Porsche concept tanks of the 245 series might be quite useful. Even more if it can be depressed enough to get rid of those pesky GIs, Tommies and Ivans trying to scratch your paintjob. Maybe adding a Lichtenstein radar for targeting/ranging.

Besides, the real purpose of the Maus was to stop Eva and Blondie complaining to everyone about Adolfs problems with the "elevation gear". A "big mighty tank with a strong, long barrel" had worked before for the Waffen-SS guys (Tiger) so....