Au contraire, with my approach, there would be 10x as many filesystems, because people would be easily able to mix-and-match different methods and plugins from different filesystems together, and if you wanted the MySQL semantics, you would mount mysql, and if you wanted the zope semantics you would mount zope.
If the early linux filesystems had taken the same attitude you have
(don't write new filesystems, only write plugins), there would be no
framework allowing the wealth of filesystems we do have, including
reiser4.