Why Mugen MBX5T kit designed accept only 150mm long bats?

[Matthew_Armeni]

The batteries you listed will most likely fit in the MBX5T kits, some without any mods. The trays will fit batteries up to 160mm pretty easily. Also, for anything bigger, you can just grind down the back lip of the tray to fit a longer pack. The three straps are what is holding the battery to the car, not so much the tray itself.
As for the ideas you listed, turning the servo would work except that you would then need a special servo horn to make it work, like the Hot Bodies D8 uses. Also, the battery tray would have to be moved away from the center of the car so that the battery could safely clear the center spur which would unbalance the car.