I would like to print with different materials.
In the case of increasing the extruder, which increases the weight of it, I would suggest that, let it uses the same system as Ultimaker 3, but each extruder gets two Bowden tube which may get connected with a "y" connector to the extruder, for example, where, when the 1st material is printed for the layer, the filament is retracted to above the y connector and the next filament advances to the extruder to print with the next filament, same case for other extruders. So, the speed and weight of the printhead remains the same and also gets 4 materials with the same printer.