Yeah, I was lax, "small subset of writing systems" is probably true, but that small subset is used by a very large portion of humanity, so I don't think that the idea that "case insensitivity" is a generally meaningful concept is a falsehood.
More precisely, I would probably agree that the concept of case is not so useful and we'd probably live well if it were only a graphical attribute (or not even that), without any uppercase (or lowercase) character in the character sets, but since the characters do exist as of now, are spread everywhere in text and in almost any case when a user of a bicameral * script (or at least the Latin one) wants to search normal text he wants a case-insensitive search, your software would better be able to perform it, and usually by default.
By the way, I refreshed my Unicode and it doesn't look like Unicode case-insensitive is that difficult, it would seem that you basically only have to perform the mappings listed in CaseFolding.txt (+ maybe the normalization steps).
* I'm ashamed to admit that I either just learned the term or had completely forgot about it
More precisely, I would probably agree that the concept of case is not so useful and we'd probably live well if it were only a graphical attribute (or not even that), without any uppercase (or lowercase) character in the character sets, but since the characters do exist as of now, are spread everywhere in text and in almost any case when a user of a bicameral * script (or at least the Latin one) wants to search normal text he wants a case-insensitive search, your software would better be able to perform it, and usually by default.
By the way, I refreshed my Unicode and it doesn't look like Unicode case-insensitive is that difficult, it would seem that you basically only have to perform the mappings listed in CaseFolding.txt (+ maybe the normalization steps).
* I'm ashamed to admit that I either just learned the term or had completely forgot about it