That sounds great! (When I used the term “Layers” I meant to refer to it the way PhotoShop uses it, where one layer can be multiplied with the underlying ones, but compositor sounds much better.
Being able to have Technical together with Archtic or rendered would be a great start too.
I use Arctic that way now, but it doesn’t have options for outlining objects, so it only works well on box objects like here:
And as you showed being able to use the zbuffer to add fog or darkness (dark fog) would be great.
There are so many situations where non photo real images communicate better than photo realistic renderings, and it can be much easier/faster to achieve a decent result.
(OT: By the way, uploading a screen shot to DeepArt can also give some very cool NPR results. You should check it out for inspiration if you have not done so yet)
Here’s an example by using your tie fighter: