The clipping plane thing is possible to fix; if I ever get around to working on the cameras, that and the FOV would be nice to have settable on a per-camera basis (So you could do zooms and such...or possibly cheat a ship out of the way by cropping it.
Soundentry and sound were never implemented because there were some arbitrary distinctions in the sound system that seemed needless, would overly complicate scripting, and wouldn't be something that could be fixed in the future without keeping those effects in scripting. So I elected to leave them out rather than to try and hack them in.
You can't render to the HUD using the camera...maybe. It might be possible to:
to get a camera onto a texture that could be displayed on a HUD. Needless to say this would be extremely detrimental to performance, as you'd be rendering two full game frames per frame. It looks like this will work without env mapping, but I've never tested it. I also don't know what would happen if you made one of these cameras point at the display.