How this would work is that any advanced computer/turtle can show these, and you have to make them as an object using code. There could be a new API for this, and people could use it to make custom operating systems.

I don't think this is necessary, the mod already provides all the tools for writing a graphical interface, and then everything depends on the hands of the one who is going to make it. But if you're looking for ready-made solutions, take a closer look at a thing called Basalt.

Do you mean that you want an API for users to make custom MineCraft GUI elements inside of the computer?

Yes.

so you mean like LevelOS's ShapeScape?

I have no idea what that is.

I do agree that this sort of project would be useful. However, I don't think I'm comfortable putting a UI library into CC:T itself, let alone a designer for that UI. Both are a lot of work, and I think the community is better placed to provide various implementations.