I've been thinking about this idea for a while now. It wouldn't necessarily be a soft top, nor would it be completely waterproof, but it would keep wind, dust and light rain out.
I feel it would be much easier to make than a full soft top, be tighter fitting, and easier to take off and put back on (than both a soft top and the shell). Simple shape of the canvas too.
I was thinking of using the shell mounting holes fitted with modified bolts with snaps in the heads to hold it down. Possibly have a metal strap across where it folds.
Cons that I can think of: Rear seats would have to be folded, not water tight, less cargo space, less visibility.
Anyone here done something like this before?
Any feedback would be great. Business partner interest?

 

They have that for Jeep Wranglers....and it's cool until it rains and it puddles in the middle and drains into rig. But, with some crossbows and running the fabric all the way to the outside of the rails, the rain would run off the sides, it'd work great and quite feasable.

 

There's a number of threads where people have done similar things. Search "kayline", "canback", "soft-top", "tonneau", etc. Lots of great tops. Might give you some ideas to even expound upon yours.