I really don't like the sound of this.
Stamina to me has always been a big no no as it just restricts gameplay. It may work in a one on one where you can manage it but fighting multiple opponents for multiple minutes in a battle situation just sounds horrible.
The new stances sound terribly restrictive as well, you cant perform an attack if you don't have the correct stance, once again may be fine if your in a one on one but in a battle situation where things are constantly changing and your fighting multiple opponents at once, it doesn't sound viable.
It sounds like this combat is geared towards duelling type gameplay and not the hectic situations of a battle environment.
The reason m and b combat is so good is that it has a basic 4 directions that you start with, every new player knows these directions and can use them from the start, its a very easy idea to grasp. To make the combat more intuitive they didn't add a bunch of gimmicks, they added functions on top of the 4 directions like chambering hilt slashing etc, but didn't mess with the core mechanics. That's why it was still accessible for newcomers and engaging for veterans.
However your approach seems to be just adding loads of things on top of each other to try and create something new and intuitive and yet still easy to play. But to me it sounds like it will be the opposite.
I'm maybe being a bit to harsh and of course I wont really know until I've tried it, but so far this wasn't the direction I thought the combat would be going.
Thanks for the video though, was very insightful.