Even assuming all four bogies are powered, you can spread the load of the
electrical equipment more or less evenly over all three cars, QR EMU
style. Remember a Comeng motor car is substantially heavier than a
trailer. The axle load would probably be about the same as a Comeng motor,
so running one of these new three car sets would have the same wear as a
pair of Comeng motors with no trailer. If you also had only one pantograph
per set (on the centre car), you're also reducing the impact on the
overhead.
Cheers
David