An old but informative article on "clefts" (the linguistic term for this kind of sentence) is AKMAJIAN, ADRIAN. 1970. On deriving cleft sentences from pseudo-cleft sentences. Linguistic Inquiry 1.149-168.

Akmajian actually gives data from three dialects that he identifies, which differ in whether the focus must be accusative, and in whether the verb in the cleft clause need agree only in number, or in both number and person. That is, some speakers say, "It is I who do it"; others say, "It is I who does it"; and still others say, "It is me who does it." If I recall correctly, if the speakers use the accusative form, then the verb following "who" is always third-person singular. That is, no one says, *"It is me who do it."