I love the 'same question on two threads' method.What's the ruling on half-elves and whatnot? They exist in the Warcraft universe, so what's the plan to include them, if you intend to?
Very innovative.
Anyhow it will probably fall down to a gamerule setting of "allow none" meaning all pregnancies between two races will fail, "allow canon" letting half elf, half humans and such that exist in the canon warcraft universe to exist and a "Allow all" rule making all possible (but since that would be a ridiculous amount of work it would probably run down to using mothers portrait and fathers racial stat boosts or somesuch).
I do have alpha male half-elf and half orc (with draenei) portraits made (since canon people of those race combinations exist(e.g Arator and Lantresor)) but full races come before finalizing those.