When editing the view label defaults in the styles editor, it would be helpful to have access to all of the text editing tools. Line spacing is a big one...Even though line spacing may be defined in the text style assigned to view labels, it has no actual bearing on the line spacing of the view label (Which is locked in and grayed out much like the rest of the other options in the view label editor dialog box).

Unless someone can elaborate on a logical/functional reason that this is not supported, I don't see why it is not? The good new is, this wont require developing a brand new tool from the ground up. Just enable the buttons that are already there.