@Facet @Felthry There's a big difference between someone standing in the way of you doing something you want, and society at large not following a particular trend. By all means, use amn't or I'mn't yourself if you like to see if it catches on. But you can't control if other people don't use it.
@Facet @Mycroft In other English dialects, the construction "I'm not" feels more natural than "I amn't", likely because of the two consecutive stressed vowels in the latter? I'm not sure, the reasoning behind that is probably pretty interesting though. But for whatever reason that restriction wasn't a problem in the AAVE dialects that "ain't" originated in. But anyway since the subject of "am" is always "I", there's never any other case to use it, so it always becomes "I'm".
-F