Palliser: zabaat, What you're saying is partly true, until the new CAN library is published. The Atmel engineer that developed a prior CAN API for the SAM3X8H, is supporting Arduino with this CAN interface for Due. Once the library is on github, everyone should start to test/discuss/contribute. And I say partly because at this very moment people in this forum could be contributing, let's say, with the design of the shield. Electric schematics have been published here. I have also shown a couple of my shield approaches. What I would like to hear in this post is: My pseudo CAN shield is ready. Here a picture of it, but I have yet to see any of them here. Does that really matter? Yes, because otherwise, you can't do any test or discuss or contribute just with the sketch or the classes. Am I right?
Oh, I guess I was waiting the same way, thinking what use is a can shield in my efforts to contribute to the testing when I have no sketch or classes. Since it's now clear that is what I need to do to get access. I will build the shield as you have listed and post it's picture. I have had 20 of the chips and 4 Dues for a couple weeks now, definitely would have built this had I known.
I already posses a good understanding of the protocol, USB-CAN adapters and debugging software tools to tackle this. I even have a project that needs it.
I would suggest making a closed project at least for people that understand it is in beta stage so you can control the feedback you get.