Hi,
I'm an active Octane for Max user.
I own Vray RT, Arion and Thea license.
I use professionally Octane 24/7, I have 12 gpus
You can't compare Corona with the gpu renderers.
If you do animations the best solution is Octane, you scrub the timeline and you get realtime results. With 4 Titans you can handle medium complex scenes with many instances.
For still life Vray rt, Thea, Arion, iRay and Octane are good tools but on really complex scenes Corona is the winner.
With gpus you must pay attention with textures. With GTX Titans you can't have more than 144 rgb textures.
I think that Ondra is working on the rt feature but I guess that the gpu is the only processor that can handle in real time many 3d raytraced polygons.
Keyshot is a good example on how use all the cpu power for realtime manipulation. It runs fast because it works in a standalone application.
The goal would be to have the Octane/Keyshot interactive speed using Corona.
regards