I'm pretty sure parsing ELF binaries is out of scope for kdump(1), sorry, but I don't think that's going to happen.
It's not that difficult to run addr2line yourself with the information provided, and that's really for the best.
You are arguing for a worse UX because of an arbitrary reason. Just link against the code in addr2line. Providing a good UX should always be in scope for a project.
How does one "just link against the code in addr2line" ?
You rename them main symbol to something else then you just call it like any other library.
addr2line is unlikely to be a trivial self-contained program without dependencies.
Then link to those dependencies.
Unnecessary. Most people's hands will be able to type up the required shell one-liner to do this.
Why would openbsd want to taint kdump with GPL code?
Then find or write an alternative. Asking people to run a command to see the file and line number is a joke.
LLVM provides llvm-addr2line and llvm-symbolizer. Of course I understand not wanting to link with LLVM code, even when the licence is ok. :)