Yeah if I ever move to a new house all the handlers are going to be in the building envelope. I'd probably only move into a single story home at this point so I guess it wouldn't matter anyway.
I just checked the attic with a temp gun - decking 136F. Return duct to the air handler - 106F exterior. Cold air ducts to the rooms, all about 96F exterior. They're all insulated of course but there's no way around heat gain being in that environment. Air coming out of the vents is 68F, barely enough to cool the rooms even running nonstop.