I don't think that the issue is minor though. As I mentioned before, this particular example from BG2 isn't the entirety of the problem. There's just too much stuff that instantly and irreversibly kill you in that game.
Only if play casually, responding to threats when they appear and bite you in the ass, instead of anticipating and preparing for them.
And that I can wholeheartedly agree with. I'm absolutely ok with having my party decimated by clever strategy that move by move defeats mine. What I'm not ok with is figuratively speaking "stepping on that random land mine".
And that's why I referred to it as bad design, which should be fixed by toning down the damage (ninja assassins should be a threat that distracts your mage and preoccupies his attention, not insta-kills him), not by adding force shields to hps.
From the Sawyer's explanation it doesn't seem that stamina is going to have any shielding qualities:
"Here's an example. Bob the Fighter has 32 Stamina and 30 Health. He gets hit by a number of attacks that subtract 25 Stamina and 5 health (leaving him with 8 Stamina and 25 Health). He is a fighter, so he chooses to use one of his abilities to regenerate Stamina. He does this and quickly bounces from 8 Stamina to 15. Unfortunately, he gets smacked again for 20 Stamina and 4 Health. He is knocked out (effectively 0 Stamina) and at 21 Health. The guys who knocked him out move to other targets.
Francine the priest casts restore stamina on Bob when combat is over. He recovers to full Stamina quickly, but is still at 21 Health. Depending on how the next few fights go, they will either have to retreat to rest or find a safe resting spot up ahead."
Both stamina and health are damaged simultaneously, and while health is damaged less, that damage doesn't seem to be connected with the amount of stamina left.
Just because some damage gets through the shield doesn't change the fact that it's a shield that can be restored fast.
As for the example, it's unclear. How does health get damaged? He says "a number of attacks". Does each attack take away a point? Does one get through and do five points? Is it a special attack that gets through the shield?
As for the shield thing... The stamina points (SP) prevent and reduce damage to HP. They can be quickly restored by abilities, regeneration (from the KS page), and spells, which can instantly revive you. It's a fast paced "modern" system with health-regen and party members getting up after fights. The casuals would love it. Underneath it, we have a more traditional and less forgiving system, which seems less important, as long as you manage SP well, and a skilled player would probably have no problems doing so.
Well, let's say it (random blunder) is a problem. It makes more sense to reduce the "blunder factor" by reducing critical hit damage in your BG2 example than by adding a force shield to your health bar. Nobody should be able to kill anyone with a single attack. See? Problem solved.
But wouldn't that in turn create situation when no spell or ability is particularly efficient and you need to literally bomb your opponent with fireballs...
You go from one extreme to another. Insta-kill attacks are bad. Attacks that barely do any damage are bad. Let's find the middle ground.
You can start by determining the avg damage and figuring out how many attacks it should take to kill someone. I'd be happy if a rogue could kill a mage in 3 attacks, if the mage is unprotected. The first attack gets the mage's attention. Then it's up to him.
What I see health/stamina system trying to accomplish is retaining serious damage of spells and abilities from IE games, but reducing randomness of engagements at the same time. In other words they would rather you lose battles as whole instead of instakilling individual characters in your party. And if you do lose characters, this got to be clearly your fault, not just concatenation of circumstances.
You don't need a fancy new system to do that.