Render to texture

In many video games it is possible to render what the camera see directly to a texture, that is what is used for example in the video game "Portal"

If this methode is imported to EEVEE (or cycles) , it would allow to do just like composition workflow work in Adobe After Effect, with multiples camera.

You could for example have result like that : youtube.com/watch

This could improuve workflow for things hard to do like motion design the way it is done in after effect for example.

Since the video texture work fine in EEVEE, i don't really know what could be the biggest difficulty.

One other thing i would like to know, is why output preferences with size isn't set for each camera instead of the hole scene like now ?