why not start with new construction / new installs?
UL489 is 40C, a therm/mag 15A ocpd might hold 18A if ambient is 29F, that could be bad on say a bc that is to some outlets that never get used and theres a fault there.
no reported issues....... not yet. the NEC is abut potential issues, not just the ones that have already happened. i like this approach, within reason and with data.
I understand where you and mbrooke are coming from, but the majority of ext installs will never cause any problems- guys, down in the south, you may drive for miles and the only set up you will encounter at a residence is an outdoor panel. And probably 98% of those panels continue to hum along year after year uneventfully, and their breakers trip reliably, through sweltering summer humidity and under the load of window ac's and under the strain of electric space heaters in the winter.
The fig 14 photo shown in mbrooke's link (cool link btw), is reflective of a bad/poorly maintained install and under the circumstances shown, it would be likely that there would be damage to breakers, bussing, conductors/insulation, terminals etc- much like the
interior panel with those few missing knockouts that becomes a toilet/house for heat seeking rodents or a palace for roaches.
Should we also ban mh disconnects also because they have a few extra spaces (which is a huge convenience for future additions) that make sp cbs/ bcs in an ext panel possible?
Remember that the NEC already has requirements for ext panels/installs that when followed effectively eliminate/reduce many of the concerns (moisture, insects, corrosion) associated with ext panelboards.
I still believe that this is more of customer/ahj issue.