From Linux NFS
I don't know why Linux finished up with such a convoluted implementation of a pseudo namespace. The Solaris 10 pseudo namespace is implemented within same namespace as all other NFS exports, i.e. export paths are the same whether you use NFSv3 or NFSv4.
The solution is really quite easy to implement within the server code. Allow clients access to the server's real filesystems, even the unexported ones, but limit their view to directories that lead to export points.
There's an old presentation on this at: http://www.connectathon.org/talks02/brent.pdf