@Dragonslayerelf: Vanilla DF only supports dwarves currently, although modding can make other races more or less playable, but typically just "odd dorfs". I believe the current hard coded dwarven ethics is a temporary measure: the Myth & Magic arc(s) is intended to support generated races, so unless you would only be able to play fortress mode as dwarves in a world that supports dwarves (not e.g. a fully mundane one, that only sports humans), support for other races has to be provided at least to some extent (and I think the various site improvement efforts currently is a step towards that goal). Slavery/cannibalism, etc. may still have to wait, however, as those are issues that would fit right in with the Law & Custom arc.
Attempting to provide a temporary answer to the Toady question then: Slavery & cannibalism will most likely remain out of bounds of the fortress mode due to the strong ties to Law and Custom, and rather weak ones to villainy (slave trafficking makes little sense without an economy). My personal guess is that both issues will have to wait until Law & Custom, but there's always a risk/opportunity that it's needed for Myth & Magic generated race support.