Nikokay; you seem unaware of the Huayan [Flower Garland, Kegon] school, Ven. Indrajala when I discussed this point with him, said the idea is that rocks and trees are the same suchness as everything else and pointed out to me this nice quote: There is no difference between sentient and insentient beings, because all things are the realization of the same thusness. A tenet of the complete teachings 圓教, i.e. the doctrine of pan-Buddha. See 草木國土悉皆成佛. [Charles Muller; source(s): Soothill, JEBD]
The Tiantai school, used Zhiyi's philosophy of ichinen sanzen
to point out the inter and copenetration of the Buddha with the world, sentient and nonsentient.
I am aware of this doctrine, I just don't quite see the point they were making. Sure, in some sense there is no difference. For example, we may say that there is no difference between sentient and non-sentient beings because both are composed of elemental particles. In this sense, there is no difference. But according to different criteria (which are arguably far more important to us on a practical level) there is a very clear difference. Likewise, from Buddhist POV all things might be the same on the ultimate level. Now that I think of it, this is kind of obvious and all Mahayana schools I am familiar with would probably agree with it. So I don't quite get what exactly is unique about Kegon/Tendai teaching in this respect. How is their position different from say Tibetan Buddhism, with its teachings about everything arising from the basis, etc?
And still, isn't it true that sentient beings have (or are) individual mind-streams, but non-sentient beings do not?