Moving the line of scrimmage back for an extra point would make the kicking game more important, which is the opposite of the direction the league has been moving in for awhile now--and for good reason. Most fans don't find the kicking game to be very exciting. It has become so specialized that it feels somewhat detached from the rest of the action.
I agree with Porforis that this just isn't worth changing. The extra point is a relic from a time when it was not a gimme play and the kicking game was more a part of the game (that's why they call it football, after all). But I just don't see it as worth the bother of changing or eliminating. It is still relevant in high school football, however.