Clinton Portis will not stay healthy long enough to break it. Carrying the ball at a rate of 350 times a year will wear him down (see Eddie George). By the time he's 30, he'll have so much wear and tear on his tires that the skins won't want to feature him and he'll be struggling to find a team wanting to take him on for the end of his career, especially with the way young backs pop up each year. Also, he's only played the full season in 2 of his 4 years and even though he played 16 games last year, he was hurt by the shoulder.
As for LT... let's say he puts up 1800 yards per year (insane number considering they will be developing a rookie QB and have defenses 8 in the box) for the next 3 years (he'll be 30 then). That would put him at about 12,700... he'd still need about 5,500 yards after that. He'd then have to put up 5 season of roughly 1,100 yards til he's 35... not likely.
Nobody in this day and age of the NFL will do it in the forseeable future, IMO.