There is no credible proof any of these styles are direct ancestors of wing chun. Please stop peddling this snake oil.
It's academic research from the last 20 years (Judkins et. al.). Most of the valuable, legitimate academic research on Wing Chun is less than 20 years old (which is why when I read old Black Belt Magazine articles about Wing Chun, they read like pure fantasy). Wing Chun is much younger than these other styles, but grew up immersed in them, and it contains a lot less material, but identical material, to styles like Hung Kuen, and what it does contain (like the Adduction Stance) is, quite frankly, some of the best, most legit Shaolin training material out there. And thus, ripe for exploitation and commercialization for a long time, sadly.
There is a rich cultural history that Wing Chun is part of that includes interactions with masters of Southern Dragon, Bak Mei, all Five major southern families, the related styles such as Five Ancestor fist. As far as ancestral influences, WC probably has about a dozen contributing styles (all of which are mentioned in the academic literature above). They are ancestors, since they are older. And everything seen as Wing Chun today goes back to people in the last 200 years who trained with those other styles, and merged them. This is kind of like the people who train MMA today, but choose to represent a specific art (for WC, Alan Orr is probably the best, but not only example).
If anything is "Snake oil", it's the stuff peddled by Wing Chun teachers for the last 100, especially in schools that missed out on things like Guoshu. I prefer to disillusion people using stuff from real historians, rather than "Class notes", which vary in quality especially around "lineage". In fact, I hate discussing lineages because nothing is more untrustworthy in CMA, imho. I often come across stuff in the literature that dismantles something older I found somewhere else, but as far as the connected lineages, that stuff is easy to show especially in the southern parts of China (because we're dealing with the more or less modern post-Ming era, rather than ancient writings and artwork which are out there, but far more open to interpretation).
Yi Gee Kim Yeung Ma like stances are found in Wutang kung fu as well. Are you going to tell me Leurng Yi or Sei Yern Kuen is a WC ancestor too?
"Wutang kung fu", is also not its own entity in a vacuum. There is really no such thing, the styles found at Wutang were also found at Shaolin. Shaolin Si was actually a major epicenter in the development of Tai Chi (Mahar). Wutang mountain just happens to be one of many where Taoism (not even martial arts, but actual priesthood) flourished.
Yi Gee Kim Yeurng Ma "like" stances are not the same as the canonical form found in the south, either. Like a lot of other southern stancework it is lower, and more body weight oriented.
If you think it's just for exercise, or a strength-building stance like Sei Ping Ma is for other styles, you are missing the point IMO. In free fighting, Yee Gee Kim Yueng Ma is most commonly executed as an action, not a stance.
Yee Gi Kim Yeurng Ma should never, ever used a fighting stance in CMA. I'd argue this with any so-called "master" on earth. Unless you completely drop the "Yee Gi" part and stand with your feet parallel, which is also a terrible stance for fighting and getting thrown. It's closest to say, the Muay Thai stance, but even that basic stance shows the risks of "Free fighting" with such a method.
As an action? Yee Gi is found in some training stance transitions (including Iron Wire, a very high level southern set). But for "Free fighting, it doesn't even make sense from a physiological point of view. It's right there in the name, "Yee Gi". A lot of people will claim to do the "Yee Gi Ma", and not realize they're missing the "二" part.
I've never heard about this type of exercise, but reads like you're advocating to be on the extreme end of the YGKYM stance like I've seen some in the Leung Ting based lines do. Probably not my cup of tea, but if it aids your training, more power to you.
I've learned several versions of the stance (the Shaolin qigong versions, the Iron Thread internal training versions, the WC version). Sure, there's a range (and more "internal"/less "external" versions are important at higher levels to avoid injury).
As far as "extreme", it's important to keep in mind the key focus of Yee Gi Kim Yeurng Ma is "goat riding" thigh squeezing strength, hip flexibility, which is why it's found in many internal qigong sets. Rooting, sure but in a very fundamental way (Hung Kuen students learn it on day with in some lineages).
One of Neigong's goals is to relax the whole body and increase mobility, while building muscle, tendon, and ligament strength. The old Shaolin way of doing this for the "Gwat" region is the Yee Gi (one of the oldest extant stances in MA history next to the 5 and 11), and it's basically the same as doing this kind of drill, but in body weight mode.
