So, going back to the principal source of the heat, air, and lots of it is the best way to cool the brake assemblies. Gear down = happy feet.
The wheel well contains hydraulic pipes and wiring. There have been problems with wiring insulation breaking down and sparking. There have been minute hydraulic leaks with a very fine spray. Put the 2 together and you might get a fire that will extinguish with airflow and then perhaps re-ignite. There's lots of oil & grease residue too. So the hot brake, or hydraulic fluid dripping on hot brake, may not be the only cause of a fire. What is the flash temp of hydraulic fluid? Could a brake get so hot on departure as to ignite it, or grease?