So, if this customization were to be enabled, I think it would become multi-mod supportive, and would quickly gain attraction through mod players on YouTube, Twitch, etc.
Another way of phrasing the suggestion is to enable transparent parts of selected entity models to become see-through portals. Lots of mods, such as the Dalek Mod, Dimensional Doors, and many others use transparent parts of entities as a hitbox to transport the player to another dimension, although not very seamlessly. If you could integrate the immersiveness to
model-specific transparent textures, that would make mod playthroughs so much better.