XFS supports case insensitive file lookups for ASCII when the filesystem was vreated with version=ci. In most scenatios with huge directories that will already help a lot. When we search for a ASCII only file we can rely on the filesystem then, only when the file we look for contains non-ASCII we have to do the hard work.
given that the parameter is called "case SENSITIVE" the option should better be named "nonascii" :-)