As promised, here are the pics:

After the seats and console came out, I found this under the driver'* seat:



Pulling the carpet and padding out showed this:





Note the melted loom and charred jute padding

Upon closer inspection of the harness, note the Orange/Black power wire for the AL7 seat harness and the corrosion:



closer:



So here is my deduction:

Cat is not clogged. May have been at one time prior to my ownership. Either that, or heat buildup over time allowed the loom to either separate or melt. In any event, the power wire wore down on the floor board (for some time noting the corrosion) and finally arced enough to start the jute padding smoldering and thus the fire. Luckily it was extinguished in time. Heat shield is going down over the tunnel, maybe the entire floor, along with new mass back carpet. Additional padding will also be put down if needed. Harness is in process of being repaired, replacing a big chunk of it, lots of fun fun splicing. Finally, as purely preventative measure, once it is back on the road, I am going to have the exhaust shop pull off the heat shield underneath and put in some insulation designed for those temps.

Any thoughts?

My thought is to ensure you solder and heat shrink the wires to make the splices have the least resistance possible. Crimp connectors (if you were planning them) are a bad idea in this case.

Only other thing I can think is that one of these wires was pinched and slightly grounding..which follows your theory. Due to the lack of "normal" issues with wiring harnesses heating and shorting out..I probably wouldn't get overexhuberant with the heat shield, etc. A good covering of loom should be adequate. Further thought...if a fire starts again..you don't want it shielded too much, leaving yourself no way to stop the fire.