I know in Isreal there is a lot of genetic work going on w/ the scaleless gene. The heat wouldn't be a problem for them, that is what they are wanting to use them for, meat chickens where it is to hot or tropical for feathered chickens. The cold is a huge issue for them.
thats where the Naked Neck gene comes into play, I have seen Broilers sporting this gene in Nicaragua and they perform much better on this Hot climates.
Do the featherless birds instinctively stay out of the sun or do you have to provide them with 100% shade? I understand wanting them for heat tolerance but if you then can't let them free range because of the sun, does it then defeat the purpose?