Also remember that this is highly WIP right now and could be changing drastically from hour to hour, and of course we’re the crash test dummies here. The materials don’t even render right now, it’s just preview. If you want to experiment with this with minimum frustration, I’d advise you to wait a bit until things settle down and there are some docs written.
In any case, this will mainly be useful for layering materials and doing complex things that you can’t do easily with the normal material system. It doesn’t make the current system obsolete, rather it complements and extends it. Be careful going overboard with multiple materials because it will take longer to render.
Nope, this is completely within Blender’s own material system design. Though I don’t know how it would affect anything once people start writing their own nodes. By the way, Ton worked very hard on making a nice elegant design. Adding a new simple node is only a few lines of code and could only take someone 20 minutes.
Will it be possible to write the shader (instead of playing with some boxes as it was on the screenshots)?
No, but there has been talk of making Python nodes, where you could write a Python expression.
And some other silly testing screenshots