However, I have a question - is it possible to skew a textures when neither the floor nor the ceiling is sloped?
The options all seem to be related to aligning textures to the floor/ceiling:

I get it. It makes sense. However, sometimes it would be nice to skew the texture even if the floor/ceiling is horizontal.
Consider the following example. On the left is a skewed texture matching the floor very nicely. However, as such things sometimes are in real life (e.g. the lines painted on the wall for patients to follow in my local hospital), a sloped wall appearance matching the overall slope of the stairs on the right might also be desirable, even though the floors/ceiling are horizontal (though, perhaps big chunky stone blocks wasn't the best texture choice here).

There are plenty of other situations where a mapper might want to skew a texture too. I was looking in the custom fields for some kind of "skew by degrees" field where a mapper could enter a numeric value to skew the texture by. Does such a thing exist, or should I move it to feature suggestions?