I don't want to get into an argument about rules or their interpretation, but I do believe the current 2013 rules endanger the parity we have in FC/F2000 right now. I'm sure the loopholes that were created were unintentional, but if someone like Scott Tucker came to me right now and asked me to design a one-off FC car under the current rules, and budget and safety weren't an issue, here's what I'd do. I'm guessing Steve and perhaps other designers have seen these same openings, but fortunately no one has exploited them yet.
I'd find a driver about the size of Fabio Orsolon, say 5'6" and 140 lbs. I'd design a full tube frame to fit tightly around him. It would likely look much like a Citation frame with a much smaller cockpit (Tim wouldn't fit). The cockpit opening would be the absolute minimum required by the rules and then I'd fill a lot of it with a removable head surround.
I'd then make thick composite panels that ran the length of the cockpit and bolt them to the frame with the 8 mm U-bolts allowed under the current FIA mounting method. I figure by using the provision that allows mounting to diagonal braces I could get at least 20 U-bolts, or the equivalent of 40 fasteners of 8 mm diameter. As Steve has pointed out, point loading is an issue with composites, so the large backing plate and 8 mm bolts allowed would make that the equivalent of about 64 of the 1/4" fasteners allowed otherwise.
I'd trust Wren's interpretation that since FIA mounting is explicitly allowed I don't have to abide by the contradicting rule that requires the composite panels not to "serve any structural purpose" and I'd argue the chassis performs "to the same level or degree" as when they are removed.
I'd increase the wheelbase by about 8" and move the front bulkhead back as far as possible (which is pretty damn far for a driver like Fabio). That would allow my flat bottom to start about 12" aft of the rear of the front tires. (The old rule and still the rule in FB, I believe, is the flat bottom is referenced to the front tires, not an arbitrary point on the chassis.)
Since there's no longer a requirement that the floorpan be flat, I'd raise the nose very high, likely as high as a 2012 F1 car, where the top of the chassis from nose back to cockpit is essentially flat. There would be a big step in the floor just forward of the driver's butt. (The old rule requires an angled floorpan like the Radon to get a raised nose, but you still need to direct air around the angled floor, and the higher you raise it, the higher the feet get, which severely limits the benefit.)
I'd use radiators with Marston cores, run a high coolant pressure, and cut the sidepod inlets and radiator area by about 40%.
I'd hire Rob Perry to do the aero design. I'll let him comment if he wants, but moving the flat bottom so far back, allowing an extreme raised nose, and the reduced cooling inlets present huge opportunities.
I'd design and make a custom billet oil pan and a billet or fabricated valve cover that structurally tie the chassis to the bell housing.
I'd have custom steel aero tubing made with something like a 5:1 aspect ratio and make all my wishbones and pushrods or pullrods from it.
I'd put tungsten ballast wherever I needed it based on testing.
I'd make all my bodywork and wings from Kevlar cloth and unidirectional fiber (at 2-3 times the cost of carbon or fiberglass).
There are a few others, but I can't show all my cards.
Nathan