Lowell has played exactly zero games at short in his major league career, and only 9 games at 2nd base. The rest of his career, he's been a third baseman except for the 5 games he DH'd in interleague play.
I don't care how good a glove he is at third--shortstop is a whole different game. Take a 33 year old guy going grey, who played his entire career at third, and stick him at short for the WS?
He's never turned a DP at second and had to avoid a hard slide there. Third base is a reaction position. Shortstops need range, and a rocket arm, and it's a longer and different throw. Putting a guy who has never played a game at SS for the series doen't sound so good to me--it sounds like a recipe for disaster
As great a glove as A-Rod was at short, even he'd have problems making the transition back now after 4 full seasons at third.