Arnaud de Rosnay sailed something like 1100 miles across the Pacific on something pretty much like a Raceboard with a swag attached for sleeping in. At night he would tie the mast sideways across the board, fit inflatable floats to each end, and set a little kite to pull him while he slept inside the "swag".
I think that something similar would actually be pretty practical (by some definitions of the term

) for the Sydney to Hobart* with the right sailor, but you'd obviously lose vast amounts of time compared to the yachts by slowing right down or stopping to sleep, as well as being slow in light winds. And if anything goes wrong you could be in trouble very, very quickly, as Arnaud apparently found out.
* I've spent days looking at the sea when racing to Hobart (5 times), Noumea (twice) etc and visualising how a board would handle it. It's much, much tougher out in the Strait than playing about near shore or in waves because of the duration you are sailing and the danger, but it's doable with the right sailor. I'd take a modified Raceboard because you need the versatile performance and a small sail, and to be honest there's very, very few people who could do it. You'd have to be top 10 or so nationally, highly trained, and have a lot of long distance offshore miles; out there at 2 am when a rain squall comes in you're in a very tense situation, very different from normal windsurfing.