for what it's worth, there are a bunch of combat tai chi practitioners out in the world:
https://www.youtube.com/watch?v=vcc0jNJwgJA
https://www.youtube.com/watch?v=vcc0jNJwgJA
I've seen people finding it very useful as an influence in HEMA where 9/10th of the difficulty lies in reading your opponent to know when and how they will attack.
It's also immensely useful for demonstrating the importance of footwork, as the last video you link to (by the English-speaking Wing Chun instructor -- even if his style isn't "really" Tai Chi) shows very beautifully.