Maybe 31 feet. I don't know. But I do know there's more involved than the physical part. Unless you get some great mutation, the size of lungs and heart will limit you. You are limited by the makeup of the human body.
Improved facilities are a factor, too.
But not forever. The long jump has been stalled for six or seven years. That doesn't mean we're near the maximum. We have come to a troth at the moment. By 2020, an athlete like Beamon with a scientific coach and strength training will jump 32 feet.