Originally Posted by Flying for Fun

Saver X, AA BE equivalent, aren't eligible for any upgrades. The same holds true for AS Elites. Fare class does comes into play, however, for immediate upgrades. The higher the status the lower the "eligible" fare class that would get an immediate upgrade after booking with U upgrade space availability. Without U space you are waitlisted after purchasing the eligible fare

Lower fare classes not eligible for the Elite Tiier are "ineligible" for immediate upgrade but will be added to the "upgrade request queue," not the waitlist, for that status. At the Elite Tier Status window those in the request queue move to the waitlist and can recive a complimentary upgrade.

James