This is pure speculation, but usually projects from the previous iClone version will work in the new version, meaning that your cameras from iClone projects will still behave the same. It's just when creating new cameras you have additional features to play with. When iClone 6 came out, most of my iClone 5 project just worked. You will most likely also have your existing lighting working the same.
I believe it will be similar with the shaders. The old materials will still work, but to make fully use of the PBR shader they will need to be converted.
What I've done with some of my older IC5 projects was to gradually convert them to get them up-to-date for IC6. Now if there is a lot of new content, then it's probably better to wait, although you can still convert external pros as that is what you need to do anyway. I do most of my character work in CC, so if you have DAZ characters for example, material conversion will be needed.
Hopefully, Peter (RL) can provide some further clarity on how this could best be handled.