Well there are also some good reasons why not to use/migrate to a metadata file system.
The first problem is that it is impossible to design and implement which only use the standard kernel file system API. The fact that it can not be implemented using the std API induce that programs which are not designed for the metadata file system must be modified to gain access to the features it provide.
Another problem with a metadata file system is that it will consume more disk space and CPU power, and therefore some user might not want to use it.
And at last, it require some time and effort to maintain all the metadata which are necessary to gain any advantage of the file system.