I think I fit into the "evolution" group, though I would be somewhat conservation in what I "evolved." I think Wing Chun is both a conceptual approach to fighting as well as an actual "style" of fighting. They go together. If you try to do Wing Chun techniques without understanding the conceptual basis of the system then what you end up doing likely won't be anything like recognizable Wing Chun. You could very well end with hard swinging Tan Sau's and rigid punches that look something like Wing Chun Karate! Likewise if you take Wing Chun concepts and apply them to something else....like MMA....it might very well be an improvement on MMA, but it doesn't instantly become Wing Chun! It might be MMA with a Wing Chun flavor, but if you are ducking punches like a boxer rather than blocking, fighting up on your toes and bent forward at the waist, and throwing flurries of hooks....then it ain't Wing Chun!
Personally I have been "evolving" my Wing Chun a bit by incorporating things from Silat and Kali. To me, these things fit the best within a Wing Chun structure and conceptual approach than something like ....Ninjutsu, Karate, or even Muay Thai would fit. Don't get me wrong, there is wide diversity in SEAsian martial arts just as any other type! The Silat I am referring to comes from Maul Mornie as well as the things that Michael Janich has come up with in his "Damithurt Silat." These have various takedowns, throws, and joint manipulations that I find fit very well with my Wing Chun, and some good ground-fighting methods that Wing Chun lacks completely. I also use Janich's weapons method or "Martial Blade Concepts" which is derived from Kali. I approach Wing Chun as a combatives method, not a sparring method. Learning to use a tactical folder or a stick is just WAY more practical than learning to use a pair of butterfly knives.
But I am not just blending things together haphazardly. I tend to keep them separated when I teach it so my students know what is coming for where. This way if they themselves chose to teach "pure" Wing Chun to their students, they can easily do so without confusion.