I think this is what Kenny is envisioning.
The two issues I see are:
The cable length from winch to bed sheave changes unless the winch is centered on the bed hinge. That may make loading awkward, maybe not.
AFAIK the rear of the bed does not get to ground level, so how do you solve the initial approach to get the load onto the roller ?
I am with Ty, a multipurpose truck that has Swiss army knife abilities is a dream. I will follow carefully any thread that takes this idea forward.
EDIT: For pulling loads onto the bed, it is possible to utilize a removable section of cable dedicated for the pull. That way the winch can be more easily utilized for rear winching operations.
Rick