Interesting video which shows us the level of Wang Xuanjie besides all the books published by this later it is hard to find footage of him.
There is an interesting remark by:

pikeamus

I’m a big fan of yiquan, but I’ve got to say that this seems ridiculous. Master wang is approaching completely open and the other guy doesn’t move… what use would training like this be?

I was myself for a quite long time against the opening posture of Wang Xuanjie even in his zhan zhuang, but recently I may revise my position, we need to differenciate training/demonstration and real combat:

1) Wang was a real fighter and I don’t think that he would approach an unknown opponent with this large angle

2) Internal martial arts are basically question of opening and closing, and for most beginners the most difficult part are the shoulders than a larger angle may help, but even in the combat for strategic purposes and to “gather” internal strength you need to alternate open and close states in our body,

3) Yiquan develops naturally a kind of “iron shirt” that means that seniors practioners are not afraid from being punched on torso to attract opponent’s attention while launching their decisive attack…

More about Wang Xuanjie’s methods and its more recent development through his prolific disciple Li Zhaoshan:
http://yiquan.chinamartialarts.net/lizhaoshan.htm
but also his Dachengquan collection of three books, presented on:
http://yiquan.chinamartialarts.net/