I put a jira suggestion for this. Please vote:
https://jira.secondlife.com/browse/VWR-1847
The idea is to create a system that would allow the interface to be as fully customizable as Worlds of Warcraft is, so that people can customize the interface on the client side, AND are able to use at least some of these capabilities (where "some" is defined by security issues) from in-world using LSL scripting in HUDs.
custom textures would make the interface seem more in-world, rather than some computer window looking in-world, which would help the immersion issue, and would make the GUI closer to seamless, regardless of which side the control is coming from.
Security issues might come into play if the HUD-based interface looks too much like the client interface, but that can be gotten around, I think.