It does seem possible, but is it practical?

It's not very practical but it works fine, too bad i had a perfect exemple project for this, that went
to hell when i lost massive data

Thing is you must think twice before building your gui otherwise if you must tweak something,
it will be so confusing that you will need to rewrite everything (probably multiple times)

Also i don't think you can make some stuff like :
- text scrolling inside a box for dialogues (and that's an important point )
- like you said, sliders

I am still dreaming of a GameSWF integration to maratis, that would solve all problems i guess

-I know I can use the maps folder to store the images for the buttons, and lua scripts to control the images.

-I can also use material/texture animation to set the different states of buttons and things.

- I can use the camera functions to control the cameras and things.

- I can create the GUI as a level which you can load into your own game perhaps.

- The GUI would be used as an overlay for a camera in your scene (which means it would be in a scene of its own)

- Sliders can also be made using material animation, but I guess I would have to do some vector math to get it to work correctly. For instance I can tie a particular animation frame to a value. There is a major issue with this I think though. There is only one timeline in Maratis editor. So it seems that changing the timeline value affects all objects globally. So I wouldn't be able to scroll one slider separate from another. I could use the 2d axis location of the slider object (if it were a 3d slider using project to texture), but that seems a lot of work for nothing.

Conclusion:
It seems that I would have to create a sort of system for this (code, objects, etc,). It does seem possible, but is it practical?

I have a few levels I posted that have some GUI elements, but I want to take it to another level.