The vertical rack I currently have mounted to my truck (North Shore 4 Bike Rack) is what most of us here on the West Coast use for serious mountain bike hauling. The advantage of them are is that they are tough as nails and really well built. Its hard to justify unless you are carrying mountain bikes (google the rack, the makers are local here in Vancouver. Their international business has absolutely exploded recently since they are such purpose built mountain bike racks). As a side note, many of us mountain bikers are picky about damage to bikes so we usually chose tray racks or "hanging style racks" like the North Shore Rack or Kuat tray racks. Our bikes are almost the price of the trucks (ok, thats an exaggeration but they are prized possessions of ours, more important than food usually).
The Kuat racks are very well built as well, and tray style. It does depend on what kind of folding capabilities it has but I have seen quite a few here in Vancouver/Whistler area where people can put their tailgates down.
In regards to my North Shore Rack, I can actually take the PIN out to 1) fold the rack and 2) lean the rack back. I have not actually done that though so I dont know how far back it will go with bikes on it and if it would let the tailgate sit flat. With no bikes on, it will definitely sit flat.
In regards to the rotating racks, yes definitely a good idea but I do question their durability and all the moving parts required. Although if you are just hauling around road bikes and stuff thats fine. When you get 4 mountain bikes (DH or AM ranging from 28 all the way up to like 45 ish pounds) that gets worrysome.
I recognize that many of these bikes exceed the price of my first car, and maybe even my second & third cars. Actually, some exceed the price my parents paid for the house I grew up in.
I take no offense at the care & love you show your bicycle, the engineer in me hates to see a fine piece of equipment treated with disrespect. I know with the bike rack I have, you would not want to attempt to tilt it with a bicycle of that caliber on it. The potential for damage and scratches would be too high.
When you go to lift the rack back up into the transportation mode, think about trying to lift an awkward 150 pounds or so of bicycles and rack and slip a pin in to secure the rack in the raised position. Awkward at least.
My experience is with my hanging style, I would not want to hang a several thousand dollar bike on it for fear something would get damaged. Granted, I suspect your derailleur & brake cables are probably routed internal as compared to my cheap bicycle with external cables. I would think that the tray style would hold the bicycle in a more functional manner.
None of the racks I have ever seen or used work well for more than two bicycles. In order to hold 4 bicycles, the bicycles are so close to each other that handlebars hit each other, pedals are in the way, etc. Again, I can't imagine hanging 4 expensive bikes on any rack.