Hi again. I'm not sure this will help, but here goes.
We suspect that the figures given out at the launch/reveal event are provisional, as the 'van that was unveiled was the only ML-I in existence and was only completed a short time before the launch event. Firm figures will probably be published in the new year.
For example, the quoted 'additional load' for the ML-I 580 shown is 187.5kg, but Hymer quoted "around 200kg" at the event. If you take the 'initial' 3015kg weight and compare it to the 3500kg max weight, though, that suggests a payload closer to 485kg.
In short, we don't have a definitive answer, we can only publish what we're told, but now you know!