I'm glad you finally removed the Warlocks, they were IMHO the most overpowered unit in the army. The new incarnation looks good.
On the one hand, I'm opposed to traits. On the other, they seem like a good idea.
Here are some drawbacks, I don't know if they are in character:
-As mentioned, limited choices on force chart (i.e. 2 elites, etc.)
-Opponents can choose to take an extra turn in game
-Opponents can choose to be attacker or defender
-Limits on units, like Jetbikes
-Can't take allied Eldar or Dark Eldar
On the other hand it could be more similar to the doctrines system, with no drawbacks but a lot of restrictions.