What's the coding background of the new IPR?

[Art48]

Just out of curiosity. I saw I think Vlado mentioning that in the beta of 3.5 a basic IPR is already working, but not all scene changes are being carried over yet.
What I was always wondering is it really true that you have to code some kind of callback for every possible change in the scene? How far is this automated or handled by the host application, max in this case? If it's true that would mean a LOT of potential bugs.
Is it true that due to the incapability of 3ds max due to its architecture to be in an interactive and rendering state at the same time, to essentially replicate the whole scene outside of max for being able to interact with it while VRay renders?
Are there some resources which shed light on the technical challenges and difficulties? I'm really curious.

[vlado]

Actually most of the problems are in our code and not in 3ds Max. So far things work fairly well actually. It took a while to rework code that was not meant to suppport iteractive adjustments, but it's totally doable. There will be continued work to improve the performance, but we'll get there.

About the rendering vs viewport state of objects, it will be an issue with plugins like Ornatrix, but we'll figure something out. Before I thought it was a bigger problem than it actually is.

Best regards,
Vlado