I disagree. Creating a strong plot point that can survive with an open ended conclusion to be used later is not just a coincidence, it wasn't planned from the beginning but the intent of expanding upon it was always there. One of your sources shows they added the WoD storyline with the intent to explore the plot point of the shards and the Source and lay the foundations for a future storyline, so of course when the time came to explore a shard they had that foundation built. That's what I'm referring to.
I think creating a world that's so defined that storylines can blend together so seamlessly as to appear to have been intended from the start is worth praise. It shows they are always trying to lay strong foundations even if they haven't decide what they'll build upon them yet. I believe that's what most of the fandom admires rather than thinking the whole game had been planned out since ten years ago.Naoki Yoshida: First and foremost, when we were thinking about Patch 3.4, around three years ago, when we were trying to decide what the story was going to be like, we did have the thought that we wanted to depict the realm being shattered. Because the realm is shattered into fourteen different worlds, including The Source, we wanted to explain that through our narrative at one point. Not necessarily for the next expansion, but we wanted to make sure we allocated some time to depict that storyline.