Hmm, I suppose it *might* have certain niche use. I tend not to read books with those character sets, and generally don't think of them.
One Topaz book that I remember getting was an innocuous copy of The Princess Bride.

Some lazy publisher didn't
want to bother converting, I guess.
Question: Isn't that what the Private Use Areas of unicode are for, and shouldn't those books use a custom font for that purpose, as part of an otherwise-bog-standard EPUB/AZW3?