I can't see the numbers in future getting any better, unless big changes are made. Many pilgrims are quite old, since some need many years to save up enough for the journey, and of course the temperature's only going to be going up (even after La Niña).
It's part of the rituals to get the timing exactly right, so it's not like it can be moved to cooler months, like has been proposed for the Summer Olympics. It is moving earlier by a week and a half each year (because of the Islamic calendar) but when you're talking 51.8C that's not really moving the needle.
I'd heard talk of health-monitoring bracelets, which seems sensible.