There is one very simple reason - no lore has been released about these lands.
We do not know the following:
- Geographical features (Rivers? mountains? forests? swamps?)
- Major populations centers
- Minor settlements
- Natural landmarks
- Cultural landmarks
- Variety of races living there
- Historical significance of certain areas
- etc
You cannot design a map without knowing this kind of stuff. More importantly, you cannot reveal the map without confirming a lot of this stuff. This is different from Araby, for which lore exists and therefore the region can be filled out on the map.
Whether GW is working on these races or not, CA cannot reveal this stuff as it will directly add to the lore of these races. I doubt GW will allow that.
Due to the above reason, I bet that either CA will never fill out these lands with even placeholder stuff (as it will have to be accurate with settlements, geography, landmarks), or they will go ahead and bring the races in with the entire lore. I'm hopeful for the latter, since they do occupy a very large space in the map.
And before someone says too minor, no lore, CA said no, please remember how some people had to eat crow when Cathay was unveiled. Never assume what CA is willing to do!