For example, LFN fails if you create too many files with the same first 6 letters :)
I'm actually honestly not sure why representing all legal FAT32 file structures is a particularly useful goal?
FAT in particular, in all of it's forms, has always had limitations and weirdness in filenames, etc.
If BigFAT was actually backwards compatible, it would've been a no-brainer to add support for in filesystem drivers. But since it changes the interpretation of some legitimate structures, adding support for BigFAT is a breaking change. I don't know whether operating systems will want to make breaking changes to their FAT32 filesystems, but it certainly seems like a bigger ask.
MICROS~1
(Long name, Microsoft Office.)
So if you create files called MICROS~2 - MICROS~0 in theory you can create enough abbreviated names that there are not available short names for long filenames you wish to create. Every LFN must have a "real" 8.3 counterpart.