Originally Posted by
Qualia
The issue with Malfurion is that his character has already been developed clearly before Legion over a number of expansions and novels. His personalities, relationships, circumstances, point of views, plots, etc. - are well established over many events. When someone whose personality is that clearly described, suddenly force him to do what he would never do normally is NOT always a good thing. Good character developments are meant to be natural and realistic. Changing just for the sake of introducing changes to the plot, in other word, forced development, isn't. Obviously, people do grow up, but it doesn't happen within matter of days (or few short weeks) and it certainly doesn't happen on someone so fixed on his path without any drastic event (which we have none). If Blizzard is to change Malfurion point of view - whether to make him a lot more forgiving / accepting towards Illidan, or the other way around, have him go full out antagonistic / murderous against Illidan, they either would need to do it gradually, or slam a massive event that can shake Malfurion's beliefs to the core. None of that happened, so it'd be unnatural for Malfurion to suddenly change.
Additionally, a character does NOT have to change to be good. There are many characters who remain the same throughout stories - Sherlock Holmes is one, for example. They are called static characters, not stale / flat, and they more or less stick to their established personalities and traits through and through. Not that I'm saying that Malfurion is a great character - he isn't (in fact, he isn't even a main character in our current storyline / arc for that matter), but introducing changes isn't always necessary and forced development is bad. If Blizzard are to keep Malfurion true to his character, they can have the brothers having an awkward meeting which lead to their cooperation, then give us a quest chain in which Malfurion started to open his mind - but that isn't a must. Too much work, for too little gain in story (not to mention these quests would be very difficult to design). Without that, there logically wouldn't be much interaction between Malfurion and Illidan, neither of them hate the other that much, but they aren't fond of each other either, after all.