Mesh Streaming

Hi guys, I have some big troubles with Unity right now.
I have a lot of unique meshes that I want to stream. And because I wanted some proof of concept I started to implement it in C#. And after trying to broke every barrier that unity had I'm hurting one that I can't pass through. Meshes can't be set inside another thread, probably because it's a proxy and need to get data from the gpu, even if I did use MarkDynamic(). I tried Jobs and my last error was this one. I tried simple task but Unity seems to complete each task before rendering (and I'll just have the Mesh problem with a custom scheduler anyway).

So there is my question: can I get the size of the native buffers without using C++? Or I should have just used a Native Plug-in to implement the streaming in the first place?