From a practical standpoint, trading DVC really wouldn't work. Keep in mind that Disney has right of first refusal for any contract that is changing hands in the resale market.
There would have to be a cash equivalent defined, I would think. And then you'd have to file the proper paperwork with Disney.
Interesting concept. Don't know how practical it would be but I can't see anything that wouldn't make it legal.
A contract is a contract. While users might have to disclose equivalent dollars for tax purposes, I don't see why you couldn't offer to pay for something with another item.
It would most certainly pass ROFR as I doubt DVC would want the boat.
Whereas the boat may be a better deal for the DVC seller than it's 'cash' equivalent.
Wonder if there's anything in the original contract that prohibits a sale such as mentioned.