I have advocated for this for a while, I think its worth a look at in the very least.
People expect it to be very limiting, but that is all up to the factors involved. How long the CD is adjustable to feedback, how long parry is, how much stamina feinting costs, how much stamina blocking costs etc.
Mordhau, being a lobby based game has "instant" swings, because it can but A) Easily readable swings, B) Unable to hold swings and when you do a swing C) There is a slight delay before the swing is executed and includes swings not flying super fast
A) is a mandatory requirement for blocking being reactionary, B) is actually not a requirement for a system like this to work and both B) and C) can entirely depend on how long you have to charge before you can release an attack and how long before after releasing your attack it is done.
These factors(attacking, defending) can be incredibly flexible to try and make it work and a tier 0 implementation to test does not take a lot to put in for testing.
Group fights will still look about the same, blocking before the swing is even coming at you will punish you, the ability to block multiple people in a row could be there with a reset of the block timer upon a successful block. You will still have difficulties when people team up against you trying to hit you from different attack sides at the same time, rather than one by one. But that part of things is not any different to how it is now.
If someone wants to play defensively they'll have to A) become good at reading attacks and learn not to be too hasty with their parries, B) learn that there are more methods and just parrying to avoid attacks, C) there are ways to play to try and keep distance between you and the one you are fighting which helps you play defensively as it gives you more time to react on enemy movement and attacks and it means you have to move less to get out of the enemies' reach.
Only critique i have about the poll and the suggestion is that you have limited the block time cooldown to 0.5 to 1s. Its obviously not a number we know if it'll work. maybe we need a shorter or a long cooldown and its a good idea to remain vague in a circumstance like that since how long it is depends on other factors and they all need to work together. Something like saying; Put a very short cooldown on blocking direction or something the like puts the suggestion better across than any specifics that we don't know if they are too long or too short.