I think the reason you didn't find it in Goodwin's grammar is that
he distinguishes attraction from assimilation. For Goodwin, as I
understand it, attaction is a syntactical modification -- the word
order changes. Goodwin states "1037. The antecedent is often
*attracted* into the relative clause, and agrees with the relative.
[Example omitted due to length]"
The morphological modification under discussion, in which the case
is converted, is termed by Goodwin as "assimiliation." And he does
cite that "1033 .... [e]ven the nominative may be assimilated; as
BLAPTESQAI AF' hWN hHMIN PARESKEUASTAI, to be injured by what has
been prepared by us (for AP' EKEINWN hA), T[hucydides].7,67."
Attraction and assimilation may occur together: "1038 .... AMAQESTATOI
ESTE hWN EGW OIDA hELLHNWN, you are the most ignorant of the Greeks
whom I know (for TWN hELLHNWN hOUS OIDA), T.6,40 ...."
Smyth, however, calls this behavior "attraction" and at 2523 he cites
the very same passage from Thucydides as Goodwin. Read also the next
section (2524) for the circumstances under which attraction/assimilation
occurs and its force.
-- Stephen C. Carlson : Poetry speaks of aspirations, firstname.lastname@example.org : and songs chant the words. http://www.mindspring.com/~scarlson/ : -- Shujing 2.35