Very interesting, thanks.
Griphoist (Tirfor) Hand Winch | Cool Tools
http://kk.org/cooltools/griphoist-tirfo/
Unfortunately adding wheels before loading an object means lifting, dragging or jacking up objects two to three times as high. I can slide a stone under say a 10" lift. To put say the little boathouse on my double wide would be a struggle.
Plus, say a bolt on or drop down axle brace could allow for wheel mounting to move forwards backwards or even sideways, with mounting on the front or back or at the left or right side.