The "Mui Fa" pattern doesn't seem to be a pattern which is particularly emphasized by Wing Chun people in Mainland, for example why many use it in HK, no school in Gongjaau nor Fatsaan seem to use it as a logo...
As far as Plum Flower stepping and the PF posts and whether they as essential and integral to Wing Chun as Jens said is an interesting question.
Personally, I think not.
For various reasons...
First question is if YM actually taught this to his students - or if it was something gis students implemented. Here it would be very illuminating to consult his senior students (or rather senior grandstudents
) such as Leung Sheung, Lok Yiu, Tsui Shun Tien, Wong Shun Leung, etc. - i.e. early students of his.
As far as I understood it from asking Gwok Fu's son about it, there is no Mui Fa pattern used in the Wing Chun YM taught him in the early 1940s. The talk about the Baat Gwa as extremely important important and is used to explain many of the system's strategies and techniques. The Mui Fa pattern and stepping as explained by Leung Ting doesn't fit the footwork and stepping strategy they employ.
Another thing - many years ago Leung Ting at a seminar, taught something he called "Lok Yip Bou" (falling leaf step) which basically says that on should place the feet wherever the situation requires and as such it is outside of the scope of the Mui Fa pattern he explains in the video you linked to (and his book).
So this pattern does not contain all stepping/footwork strategies of Wing Chun, at least according to Leung Ting's teachings.
Do other branches of Wing Chun have Plum Flower footwork? YKS/SN type Wing Chun - or at least the school/branch I trained in for 12 years didn't teach such footwork, or used a plum flower pattern to explain footwork strategy and techniques - doesn't. Yiu Choi branch? Would have to ask about this some time...
As far as the actual plum flower posts (Mui Fa Jong), it seems this is a sort of generic training "tool", more relating to acrobatics than fighting skill.
Anyhow, training on those posts doesn't allow for flexible, versatile stepping with the adjustments dictated by an actual fight, so training on those has no relevance to developing practical stepping/footwork for application.
In the final analysis, this pattern might be a convenient tool to illustrate certain aspects of a given system, but a fundamental, indispensable thing that encapsulates the style's footwork and allows it to be used "as it was meant to be" it is not, far from it, it seems.
Btw, Jens, which style of Wing Chun do you practice, where this pattern is of such importance?