In this demo by On-Set Facilities, we see green screen (chroma key) VFX being rendered in real-time. On YouTube, On-Set Facilities adds:

This is a great PreViz tool, so that we can record in REALTIME, the FG, the BG, the Matte, and the Camera Track data (in FBX format, with zoom a focus) so that we can finish in NUKE the final composition with the OTOY same ORBX file we used for PreViz in UE4. Credit ‎Oscar Olarte Ruiz. Pre Vis, After Effects, Maya, Autodesk.