I actually just finished developing an interface between Julia and .NET for an internal project based on information from @oheil .
When I started that, I was a newcomer to both Julia and C#/VB.net so it seemed infeasible with the C interface.
So I did it using communications over pipes, like a client-server communication.
Though this takes time, (de-)serialization seems to be fine (i.e negligible to the user) in most cases, even with relatively large arrays (about tens of thousands of double precision numbers).
I do not know if you tackled this issue already but the main missing part for me in the documentation about julia’s C interface was how to use it properly to load and interact with modules and how to handle special types. I was completely lost i the whole packing / unpacking of pointers to structures…
Also, there are some base types that exist in Julia that do not in .NET, so some conversions need to be done explicitely. For instance I discovered that my .NET (maybe it is a matter of version) did not support Int8.
Keep up the work ! Cheers !
EDIT : See this answer from @Shuhua maybe its worth converging on this Correct process to use julia code from C# or VB .NET - #17 by Shuhua