I don't know how close leaving an undefined method as described above to the class designer comes to automated merge. Note that at no point I'm arguing that the body be merged. I'm seeing guarantees that the type system tries to hold up in favour of the users of roles.
If you're not using "multi", then the signature is superfluous for type-checking purposes. That is the purpose of not using "multi", after all: to avoid the overhead involved in using the signature in method identification. So either you use multi, in which case the signatures exist in parallel; or you don't, in which case the signature isn't important. -- Jonathan "Dataweaver" Lang