Hmmm.
I watched the videos and see nothing to change my mind.
Then again, I have been riding in the sand for almost 40 years.
As far as your bike sinking with a standard paddle I have to wonder about your experience riding in the sand.
It sounds like your bike was not set up correctly or, you weren't going quite fast enough.
I have rode hundreds if not thousands of times in the sand and I have no problem with my bike sinking.
Then again, I might be a purist
Don't get me wrong, it might be fun to ride something like that just for kicks but it would take a lot to convert me to a true believer
http://oem-cycle.com/AROUNDTHEWORLDONAKX500.aspx