They haven't, but a Keystone filter (on its own or, perhaps, as an addition to the Perspective filter) would be wonderful. Even it only handled a pair of verticals or a pair of horizontals, that would work well. If, in addition, such a keystoning filter could apply itself as a "percentage" of the stated correction (in order to leave a little bit of keystoning in order to look more natural) that would even be better!
