Can I write my own shaders now that UE4 supports forward shading?

I want to create a cel shader. I thought I would be able to as long as I used forward shading, but I don’t know how to do this or even if it’s possible.

Bump, want to know if its possible to use the light direction in the material editor with the forward rendering or if it could be a posibility in the near future.

Meanwhile: Toon shading model - Work in Progress - Unreal Engine Forums