The AED is not exactly something any backpacker would want to buy or carry
My wife is certified to teach CPR, 1st Aid (adult & pedi), AED, and other type courses. She estimates that some of the current AED's weigh about 7lbs.
As with other electronic instruments, could they be eventually be made in the 3-5lb range?
If so, you might find them being required for certain group expeditions (such as BSA high adventure treks).
All three of our crews were trained in 1st Aid/CPR/AED and at least two members from every crew were trained in Wilderness 1st Aid.
Having an AED might mean the difference between life and death for some (even apparently healthy young people).
But I agree with OM, I wouldn't want to carry one at this time.