This is definitely heading down the right lines, but one crucial thing is missing - the rotation of the label isn't accounted for in the bounding cuboids, which means that the layout is generated incorrectly. To illustrate this, run the basic example, set the Y-axis title to "Vertical", and put in a long title. It's clear that the graph area is reacting to an increase in only the horizontal (un-rotated) size of the label.

Oops! Yes you are right - I hadn't thought about that.

Regarding this, at which point do you think the rotation should be performed? In reference to the boundingCuboid function i.e. during the construction of the basic cuboid, or when returning the final cuboid etc.

I think I'd be tempted to add another argument to the second boundingCuboid() function (the one which currently takes the anchor point) and do the rotation there. The rotation centre should be the anchor point, incidentally.