Hello gentlemen,
I think this discussion is going a bit too far and maybe we are losing focus on what does really matter.
My thoughts about this spinning vs turn cap quarrel are very chill;
in my opinion it doesn't matter what will be the path which developers will choose,
but i really care about the final game experience quality.
As far as could read in this thread, if the issue was IRL, there were absolutely no problems.
Who thinks that sword spinning is useful would be happy to use it and showing it off (the witcher guy video example),
who thinks that sword spinning is dumb and useless would be happy to fight against (the capoeira bad ending video example).
Videogames like Chivalry and Mordahu showed us that the real problem stands in code implementation and not in spinning itself.
In Chivalry, I remember, spinning literally killed the whole game experience, it had no movement restrictions;
players could do Horizontal 360° combined with Vertical 180° while crouching with absolutely no inertia all together in a little fraction of second.
The final result was that the spinning animation wasn't smooth, like the one from the witcher guy video,
but laggy and irregular instead, making spinner movements unintelligible.
All that without even mentioning the negative dragging, by doing it a player could chop off your head by swinging a sword at the absurd speed of 0.5cm/second, technically a caress.
Honestly i even understand who dislikes turn cap and movement restrictions, because in many cases they slowed so much the game, making duels boring and taking away the possibility of a decent crowd control in large battles.
TL;DR Version
case A) Spinning will be in without any movement restriction but with insane speed limitation; we can only hope that server-client netcode, server tickrate, client rendering will work in a so exceptionally good way that Spinners movements will be intelligible making them capable of being avoided or countered by a normal human being.
case B) Turn cap or any other movement restriction feature will be in; we can only hope developers will make a very good coding job, having a formula that will calculate a smooth movement speed coefficient curve on client side, that will be synchronized (validated) even on server side to avoid any type of bypass (cheating).
case C) Very hardcore PVPers will find and abuse every unbalanced move/hit/technique making the game frustrating for anyone else (as Chivalry shown us). Solution for non-abuser player: just play for gathering-processing-crafting-merchanting, or start cosplaying Robin Hood by killing all players mechanic-abuser by ranged weapons making the game frustrating for them.
That's my thoughts, maybe I'm wrong, maybe most of you, if not all, will be in disagreement; but I played thousands of hours on medieval fighting online videogames experiencing different types of gameplay. Surely I know what i want to play.
Sorry for the wall of text.