So if you haven't heard, New player models are 25% done and will very likely be released in stages. This could be the best approach because it could mean some much needed time devoted to each race and even mean the introduction and availability of a minor race related to a main being finally playable and accessible.
How? Well, the models take far longer than phasing an existing zone for 1 to 6 levels and adding a few quests.
Secondly, if you're taking all that time to redesign a major race, it is relatively one or 2 minor cosmetic changes away from being a minor race. and have another team add some quests and an intro narrative to start the minor race. You don't need a new zone or a huge deal like a full major race does since a minor race is tied to a major race and can/should share capitals and most of the earlier zones. You could eventually have something like this.
Blizzard spend ages re-doing new orc model - male/female incl new and extra animations etc.
Easy to add Mag'har orc by simply providing a brown skin tone range and some tribal ornamention accessory- animations don't need to change
Easy to add Dragonmaw orc by simply providing black/grey skin tone ranges
Slap on a sub menu after selecting orc on character creation to display options for green orcs/brown orcs/black orcs and you're there
Wanna be special? Then add a phased level 1-6 version of Twilight Highlands for Dragonmaw and Nagrand for Mag'har orcs.. with a shor story line that has them packing to Durotar after level 6 to join the regular levelling trail.
make the phase 1-12 instead of 1 to 6 and you can sell it as a major attraction/feature of the next expansion - which would have minor races and not just "new character models" even though it's the same thing.