In the quest for a modern user set of hollows and rounds, the desire is to jump in and address the body. Likely, most of the opportunity lies in the iron. Still, it doesn't hurt to start thinking about bodies that might work well. To that end, I'm excerpting some images from a pretty good book I picked up when I was fortunate enough to visit a Lee Valley store.
Also if you haven't already read everything at http://www.planemaker.com and seen the Larry Williams video, that's solid baseline information.
One example from this book ends up with similar geometry as English planes, but creates the mortise by laminating strips on the outside.
In the next example (opening bouvet image) from Roubo we see the construction even more simplified, with the mortise being completely open on the side. (Dig the horn and the side facing wedge too.) I do wonder how bulky this style would need to be on wider molding planes, or if there is a tendency to warp away from the open side causing tracking issues.
The first shows using this motion to restrain the iron, replacing the wedge with a simple inexpensive carriage bolt. Dowel pins of a sort are used to keep the 2 parts aligned.
In the second, the wedge secures the iron as typical, and the heel-toe motion allows mouth adjustment (much less important in molders) The alignment is controlled via the simply created dados in the toe and laminated construction.