The problem is when you get close to the MTOW in the van, she ends up with an aft load and you need to put the trim forward of the T/O range to stop her over rotating on T/O.
I can only imagine that an increase in T/O weight will have the two rear seats occupied by Adults rather than kids and compound the problem. Maybe with the pod equipped vans it may be okay if you can get the weight forward.
I often used to think that the rumours of the 150KG dispensation was one started by the operators to push the numbers a tad more than what you would in a similar lighty. We all know the van is very capable at weights higher than 1814kg, i beleive the wing was designed for 2100kg, but i for one would not be interested in a heavy airvan up north on a gusty humid day.