I don't know if it is possible to add a big green billboard to use as a green screen. I'm guessing a skydome would mess with the IBL lighting.  But the ability to make a green screen  would make compositing elements from FlowScape more flexible.

Hey braj

Change your sky brightness all the way to the left and you will have a black sky you can use for chroma keying

Ah, that works! Thanks!