So if multiple 100A panels are OK, what would be wrong with two 100A feeders off of a 200A panel each feeding half of a dwelling? How about 3 100A panels from a 320A disconnect each supplying 1 floor of a large house? This seems to be the issue -- at what point is a feeder supplying a diverse enough portion of a dwelling to qualify for 310.15(B)(6)?
This seems difficult to codify easily as it would be possible for the dumb electrician to put a bunch of electric heat, water heater, and one 15A outside branch circuit all in one panel fed with #4 copper. Conversely, if all of the general purpose branch circuits and all of the required ones that have no calculated load (outside, basement, bathroom, etc) were put on a 100A panel with #4 copper, you'd porbably never have more than half of that being used for any significant time.
