That is a good idea. Sounds like you are going with a similar pivot method that some of the high end bike hitch mounts from Yakima, Thule, etc. It would be a major welding, cutting and fab job to do it right. Take a look at the Maximus 3 web page. He has a high end shop that custom designs aftermarket parts for the Wrangler. I have a bunch of connections for steel fab shops here locally, but that sounds like a major project. There is an open thread somewhere here that talks about a company that makes hitch tire carriers for other vehicles. We need to locate that thread.
I have an Idea but no cad system to send you picks from. It is a spare tire holder that mounts to the tow receiver on the Cherokee. use a 2" shank with a hinge on the end that will rotate 90 degrees from vertical to the horizontal parallel with the rear bumper. On that Hinge have a 30" square tube with an additional 30" tube that fits over the other 30" tube so that once the mount is tipped horizontal that it can be slid over so the hatch will open. with a retaining slot, rod, to keep it from sliding off the end of the tube. Remember to have a locking pin to keep it in a vertical setting while driving. If you like the idea let me know