Requesting support for connections to/from UNIX domain sockets for the -D,-L, and -R. The support for hosting sshd on domain sockets and connecting to these would also seem beneficial.
Domain sockets offer great flexibility when compared with traditional, port based sockets. The OS can offer filesystem based access controls, rather than each application that uses the sockets having to implement it's own authentication/encryption scheme.
My specific use case is to securely forward the domain socket used to connect the Tor daemon and it's GUI controller, Vidalia. This way I could elegantly control the Tor daemon running on a headless server on my desktop.
A patch for OpenSSH4.7 is here: http://www.25thandclement.com/~william/projects/streamlocal.html