When I am not bound by a style that mandates otherwise, I like to use whom in dative constructions and who in accusative constructions (I am aware that English doesn't have a proper case system, but it is convenient for the purposes of this qn). Let's call this who/who/whom usage, matching nominative, accusative, and dative respectively. This appears to be moderately widespread, the death of whom notwithstanding. For an accusative example, consider Is there anyone who I could ask? vs. Is there anyone whom I could ask?
Are there authorities who explicitly recognise the possibility of differentiating between the accusative and dative constructions in this way? To document what I have looked at so far:
- APA 6th stands by the old-fashioned who/whom/whom, saying "Use who as the subject of a verb and whom as the object of a verb or preposition" (3.20). Chicago 6th has a very similar formulation (5.63). The Economist style guide has a nice discussion explaining its identical prescription.
- Butcher's and New Hart's Rules both say that grammar should be correct, but say little about what correct grammar consists of. I think MLA also doesn't prescribe on this point.
- Fowler's 3rd articulates three rival views, namely that (i) who/whom/whom is moribund, stifling, or artifical, and who/who/who is the right usage, (ii) the righteous who/whom/whom should be defended against the slacker who/who/who, and (iii) who/whom/whom is appropriate for written language, but who/who/who for spoken language (from CGEL). Fowler's further talks about tricky issues about the use of who/whom as a relative pronoun vs. as an interrogative pronoun. Fowler's makes no prescription about this. Who/who/whom is defensible according to Fowler's reasoning, but the possibility of this usage is not discussed.
Bonus points to anyone finding relevant guidance from CGEL.