It would be really sick if we could use an image or a gif or something as a mask for the portal. Masks are often used in video/photo editing to define an area to cut out. So we could use an image (or a gif for a spinning/moving portral) to cutout what the portal is shaped like, that way we could do something like make a portal shaped like a wormhole or some other kind of portal.

It would also be cool if we could supply image or gif overlays on top of the portal to do things like make tentacles coming out. Or perhaps this would be better suited as custom portal models?

I think these features would enhance the potential of this mod by making them feel more immersive and natural to the game scene (especially for map creators)

It's probably achievable using the GUI portal feature