The experiential reality of unity comes with enlightenment. But clearly this has not materialised into actual unity of religions and spiritual paths. Many seekers and teachers agree with the idea of unity but are incapable of moving into a single shared understanding that would give the basis for Actual Unity. That is why Actual Unity is the work of Consciousness. The New Dawn lays the foundation for Unity, but it will take a very long time for it to happen unless there is a dramatic change that gets everyone's attention enough to provoke a shift in dogma and beliefs.
Spiritual beliefs are abundant, and often irrational and sacred to the believers.
The synthesis of advaita and Zorba the Buddha has little support from either camp. They are natural antagonists. And it will happen.