Why is GUI Texture deprecated in Unity 2017?

My project relied heavily on using GUI Texture to display 2D pre-rendered backgrounds behind 3D objects using an extra camera and culling masks to display the backgrounds as layers on a separate camera meant for rendering 2D. On upgrading from Unity 5 to Unity 2017.3, I come to find that the GUI Texture no longer works according to as it should.

I tried substituting this by adding a Raw Image from the UI components, but it did not work as expected.

This is rather frustrating and disappointing as my project relies on having pre rendered backgrounds and it seems there's no other way around this using the recent version of Unity...

 

Hmm, for now it seems the only solution is to add a Screen Overlay script to the 2nd 2D camera (downloaded from the Assets store).