Quite frankly, I'd be interested in a solution that would allow me to take my hard top off by myself, lower it safely onto a cart, and that didn't need to be mounted to a fixed structure.
The question is how much it would cost and how reliable it would be. Something that plugs into the hitch receiver sounds like a good concept, but when you start packaging and shipping heavy steel tube needed to make a crane it gets very expensive very fast. You could possibly design and build something for $250 and spend $250 on shipping. Add on a margin for insurance, returns, warranty, etc., and of course profit to make it worth your time and effort, this might turn out to be priced out of the market.
If you can work out a business plan to produce at a reasonable price I might be persuaded to buy into a Kickstarter.
I'm a JKO Reject