Surely someone could come up with a skid system and then various mounting kits for different vans? You can buy towbars for every vehicle so why not a mounting kit to fit a universal base? Even if it was the strongest type ratchet straps to hold the base this would give you some adjustability. A car transporter can carry various different vehicles and likewise a flat bed can carry different sized and shaped loads securely.
All vans have a chassis running under the floor so maybe four adjustable mounting points could be drilled through the chassis?
Now this is a very good point!.
Its one of Yes and No answers...

Let me explain -
You can buy a towbar which is universal - it will fit a mini or a Range Rover. You could link up a 6 berth carvan to this towbar.
That does NOT mean to say a mini is capable of pulling such a large heavy load safely....
This is what I meant by 'standard' and 'bespoke'. Just because we can physically get a system into our vehicle, may not actually mean it is wise to do so.
WFP is becoming more common and more systems are being built/sold. This will increase the likelyhood of accidents of vans with WFP systems. I would expect HSE to take a very keen interest in a few years time. No doubt we'll end up with a set of guidlines (not unlike van mounted cherry pickers).
At the moment, the WFP industry is still fairly small and we're flying under the HSE radar.