This sounds like a very useful tool. In Clang, we've been very careful to maintain an abstraction layer over different Objective-C runtime implementations. Your email talked only about the Apple runtime - do you already have an abstraction layer for the runtime-specific details, or is this something that will need to be added prior to upstreaming?
There is an abstraction layer to allow runtime-specific implementations but it is possible that you need to tweak some interfaces to make it working for all your use cases. I design the abstraction to accommodate both macho object file and llvm bitcode, which are two completely different underlying implementations.
I just post the code review: https://reviews.llvm.org/D59945 and I also added you as code reviewer. Let me know if you have any comments and suggestions.