I also don't intend to sound rude or apathetic, but if someone has stress issues with things that happen as a course of normal gameplay in most any game out there, they really should be reconsidering their choice of entertainment.
@the OP:
Certainly there are going to be situations outside of end-game/raid content that could possibly stress friend out. How are they going to deal with that? You can't keep asking SE to create an "easier, stress-free version" of every single type of content that your friend happens to find is stressful to them.
Also, the idea that MMOs are supposed to be inclusive is certainly true... but to say "that obviously includes people with stress disorders that are triggered by playing intense content" is a bit of a stretch. If you're going to cross that bridge, then what's to stop people with other disorders from doing the same?
I'm sure there are a number of things in your friend's life that they've had to come to terms with, or find other ways to engage in or enjoy due to their condition. I doubt your friend asks everyone they deal with to please alter things or do things differently so they don't get stressed out.
Again... I empathize with your friend's condition and I'm not just saying "pffft... screw them". However, at the same time... it just seems something that could be a can of worms.
Let's say SE does that. They say "Okay, in order to better accommodate people with stress disorders, we are going to introduce easier versions of all content for people to do".
How much would people like to bet that, "overnight", a whole bunch more people who never complained of it before, suddenly start popping up with a variety of disorders of their own, and who require special consideration by having SE change some aspect of the gameplay to suit them? I can definitely see people abusing such a thing, given the behavior already demonstrated by many of them.
What's to stop other people from claiming they have issues that requires them to avoid "this" or "that" and so SE needs to change some aspect of the game to suit them? What is SE going to do, check the medical records of everyone who claims they have an issue to see who's lying and who's being honest?
How does SE say 'Okay, we'll accommodate the people with "List A" disorders... but not those with "List B" disorders". Then they're going to be accused of favoring some players over others.
And further, how long do you think it will be before some of those same people are demanding the same rewards as those doing the toughest version of the content in question, arguing that "I'm being punished for having a medical condition! SE is punishing people with legitimate medical conditions by refusing them access to the best gear in the game!!! SE doesn't care about their customers!!"
FFS people without any kind of medical condition are already making those claims. Could you imagine the less honest folks out there having access to such ammunition as saying "I have a medical condition"?. They'd be all over that.
It's a potentially slippery slope, to be honest and I can't see how SE could reasonably handle it without painting themselves into a corner or coming out looking like the bad guy at some point down the road where they finally have to draw a line.
I'm not saying "it shouldn't be done". I just don't know how realistic a thing it is to expect, given the time/work involved, and the potential consequences of it.