We already use Tau for both torque and for shear area. The nature of both types of calculations typically involves circles, and therefore, pi. Yeah, I'm nitpicking, but the last thing I need is for my simple calculations to have three different uses of the same damned Greek letter.
Everyone knows pi. It's too late, it's been the standard for generations. The same goes for the English language - it sucks, but even though it makes logical sense to change to something better, good luck trying to get everyone on board that train.