as of now yii2 is currently under alpha release it is not ready for production it might changes its source significantly and the visual rbac might be unavailable. so dont go for production with yii2. if you wanna give a try you can play with yii2 but not for production
By ‘No yet’, you mean existing framework classes and extensions are reasonably solid to the point where they can be used as the basis for a module or are more changes planned?