Admins should receive an error message when theres reserved terms conflicts. when the
register_taxonomy() or other
register_foobar()'s first get registered into wordpress
"Warning your taxonomy x conflicts with a reserved term. see ... for more information"
Especially when in the codex itself it says:
Doing so can cause WordPress to respond with a 404 error without any other hint or explanation
I would be more than happy to join the building team to implement this!