We are of course free to go away from the ePAPR flat device tree (we did already to some extent).
I am not talking about the ePAPR flat tree. I am talking about the flat tree as used in PowerPC Linux for many years now.
I agree with Segher we should stay close to the "original". That's why we used dtc for our device tree creation to begin with. It has a recognition effect, making it easier for others to join in.
It's also well-proven technology. And lastly, wouldn't it be nice if we could hand-off the DTB to the kernel at boot -- bye-bye legacy interfaces.
Also, at some point we're not writing the DTS manually anymore anyways, so it doesn't really matter ;-))
You'll always have to write some of it by hand, in one form or another, for some system-specific devices that cannot be probed or that you don't want to probe for (PHBs, I/O bridges, ...)
Segher