The existing wildly popular library with the same name that conceptually overlaps, well, a lot of what libmui is and does, more or less has been a required third-party lib on its platform for nearly every piece of software written in the last couple of decades. Barring software that's written directly against raw Intuition, that is. Not much is, any more, so I can assure you there are millions of people out there—millions, I tell you!—who are going around looking to update their libraries.
In order to avoid confusion with such a widely-used piece of software, consider the option of renaming.