Sure you can. There is even a “Suggestion” category for this!
About the vector type, there are of course multiple options, but I think it should be quite straight-forward to add
float3 as additional supported property types.
Currently there are two ways to color polygons, but probably not in the way you mean. You can set a color based on their type in the Object Types Editor, or you can set a color on their object layer. But this just changes the color of their outline and the transparent fill, while I assume you mean to have the ability to have solid filled or textured polygons.
I think it would definitely make sense to extend the use of polygons to include visual use-cases in addition to annotation purposes. But this will also raise several questions:
How should textures polygons behave on isometric maps? Probably not like the current polygons do, which is to get projected onto the ground (it may be a strange coordinate system for visual polygons).
If you’re going to use polygons for visual purposes, don’t you really want to define meshes instead? Otherwise you can’t have holes and meshes are easier to render. But of course meshes are more complex to edit.
For textured polygons, how should the texture be mapped to the polygon? Maybe again we’re rather looking at meshes where we could define texture coordinates.
Or maybe we should keep it simple and just define a kind of texture fill which the polygon will clip.