Just cautiously kidding. Aluminum starts to soften and melt at around 1250 degrees.
The gentleman making the mufflers has already made quite a few aluminum exhaust systems that have lived for years on project cars. It's all in making them start at the collectors and going back from there. The trick is to have them be as large diameter as possible so that the heat expands and actually cools better. They won't survive if they are 2" or 2-1/2" because they will hold more heat.
3" is the starting minimum.
My exhaust is 3-1/2 anyway to the X-pipe and then it narrows down to 3" all the way back where it ends and dumps just before the rear end differential. No tail pipes needed.
The only reason that manufacturers do not have them be standard equipment is probably the same reason that P-body mentioned. The exhaust gasses being as they are, carry a lot of toxic corrosive properties, so systems may not last as long in theory. My car is a week end thug, so it does not see many miles in a given year anyway. Aluminum does not rust, but it can oxidize and grow spores in a way.