I see what you mean. And I also think, that they will have other rendering options available.

Currently you already have lots of rendering options. You can render with no lighting, with vertex lighting, with shadow maps, with pixel lighting and with a combination of shadow maps and pixel lighting. Probably deferred rendering will be just another option.

The built-in shaders can be changed currently. There is a cross-platform shader language in Unity. But we will see how this changes in Unity3. I am very curious about it.