Sorry for the delay, I had to try out different methods including proxy for arnold.
Yeah that works too (hopefully it won't crash on me when selected)!
I tested on Arnold for proxy with latest version I just updated and it's very fast opening and rendering with no issue (sometimes it crashes and I think it's Autodesk's fault).
In your previous method (export FBX with preserve instance option checked with Vray proxy), it is very slow opening the fbx file in Maya and 100% it will crash even if it is 8mb. But when I open it up in Blender just for curiosity and oh man...it opens very fast and not sure how Vray rendering works in Blender because it always crashes on Maya. I'm not a Blender user but I feel like Autodesk is the one that messes up everything, the more problems I know the more I know it's from Autodesk.
When I compare the speed of proxy export between Arnold and Vray after "Instantiate", Vray takes a long time and it's pretty worrying that it could crash anytime and will never finish the line. For Arnold, it's pretty fast to create a file and I think it is because the original obj is a proxy and it allows you to export all proxy objects but Vray doesn't allow you to do that. So I guess Arnold is the winner here. But it's not enough to give me everything what I want. The best way is to use Max as final render with new shader but I'm very curious when someone wants you to bring a scene to Maya with materials and everything in it. How are you going to survive through crashes, slow and frozen? Any advice for this situation would definitely makes my life easier!
I personally think it would be better for Itoo to have standalone like SpeedTree and that's just my opinion of course, because I believe it is a very unique tool and shouldn't be fallen in the wrong hands (Autodesk...lol).