Thanks for taking time and looking at the drawing.
As I stated this is an example to show the result of increasing hitboxes.
About the impenetrable blocking region, I know that the hexagon results in the attacks from the frontiel half space to be blocked but that was just to show that you will be able to implement 3 different (actually two since the sides are symmetric) outcomes of the block.
Instead of using the hexagon let me add two more boxes.
http://img22.imageshack.us/i/octablock.png/
As you see the blockable region is no longer the half space and you have open unblockable side hits.
The side blocks here are transition for blocking. It should be worse then a frontial block but better then an unblockable side hit for the defender. Lets say when the defender is blocked this way he can continue blocking but takes damage and can NOT attack for a small amount of time hence the attacker can hit again. Again we are brainstorming here so nothing is absolute the important thing is now we have transition regions and more variable, smooth outcome in blocking.
Let me give an example of its advantage over the current boxy model.
http://img24.imageshack.us/i/blockdiff.png/
As you can see there are two cases which are very close to each other. In the first case attacker hits the frontial plane and blocked fully but in the second case where attacker is in a slightly shifted position but the defender just gets kicked away.
This is a very very drastic difference for a very slight change.
In the more quantized model the attacker hits side and the defender somehow blocks the attack for both cases. Even if the slight shift changes planes the difference between somehow blockable to blockable or somehow blockable to unbockable states is not as drastic as the change between a totally blockable state to unblockable state.
So far we've talked about the idea.
I aggree that this may need good amount of change in the code. I think there maybe solutions for implementing similar idea with a less amount of code.
In terms of computational power, even computers of 4-5 years of age should handle the additional load quite easily. Afterall the graphical enchantments I have seen so far are computationally much more complex then this.
I think we will talk about on this more.