Actually, this has been done.
The ATD diaper is essentially a prefold cut to the shape of an all in one with PUL on the outside. It closes with snaps. Here's a pic: http://store6.yimg.com/I/babynmore_1761_79706
and a line drawing: http://store6.yimg.com/I/babynmore_1761_141800
Is that what you're thinking? Were you looking for an all in one made of prefold material?

and a line drawing: http://store6.yimg.com/I/babynmore_1761_141800
Is that what you're thinking? Were you looking for an all in one made of prefold material?