Requests for Toon have popped up over the years, for sure; however when compared to our USP mentioned earlier about photorealism for archviz - toon is not realism, and has a more limited use in archviz, which affects it's ranking in priority. I know for some Toon is really important, but in our assessment when you look at archviz projects published anywhere from Behance to CG Architect to Artstation, very few use such a shader. Again, this is just to give an insight in to how we assess things in terms of priority, not to say that someone wanting a toon shader is wrong - just that we have to consider that request inside of a bigger, particular picture.
This is different for V-Ray of course as it is very much a general purpose engine that gets used for all sorts of things, and Toon is much more widely used in that regard. Naturally those who request Toon will see it's priority differently, and naturally it would sound like they have projects and work where it would be a fit else they wouldn't request it, but overall we've felt that other things take the lead in terms of the target market and use of Corona - so the request isn't ignored, just that is how we've assessed it so far when we choose what to work on for the next release. Sorry to those who are disappointed at not having such a shader yet, of course.