This tip from Ahmad Shadeed is interesting:
CSS Writing Mode
In the past I’ve used CSS transforms to do this. I actually prefer the text to face the other direction, so maybe transforms would have to be used anyway.
For me, though having had a website with vertical (side-on) text for years, I’ve actually grown to dislike it; I’m not sure why though.
Still, vertically stacking icons is a great use for it.