Well just an update on my system:
Currently the server can create the following on the client:
GuiWindowCtrl
GuiTextCtrl
GuiBitmapButtonCtrl
GuiRadioCtrl
GuiSwatchCtrl
GuiScrollCtrl
and so far no security issues. The command for the button has been restricted to only be one commandtoserver so you can't call anything on the client. The only issue with this is that you could in theory flood the user with GUI files, but you can do that with shapes/textures or whatever so i'm not too concerned. I'll put a flood control on it.
Once it's done and thoroughly tested, it should be a mod for both the client and server to download. Then in the GuiControl of the GUI, you just put a "sendToClient" equals 1 and when a client joins, the server will send him the gui for him to use when he spawns.
So far so good.
