As much as NPCs and a quest line would have been interesting to see in the beginning, it would have been a smarter move to focus on adding in more multiplayer features. Features like different character interactions, more equip items, more customization options etc. I don't think a lot of people would get much use of a single player mode unless it was being updated constantly and that would have been a lot to maintain. Multiplayer has always seemed to be the type of gameplay that IT and FH both had. I think I would have rather seen more expanding on the features that help multiplayer games captivating and successful than a single player option.
Interesting! I do agree that multiplayer modes usually last for a longer time, but story/single player modes usually come to an end eventually. People usually only play campaign modes once, then never play it again after they beat it. And with Kovu's dissappearing act and the staff not having the source code, keeping the story mode updated would've been a nightmare
However, I really enjoy thinking about what could have been!
What would the NPCs have sounded like? Or looked like? What was the story? Who was the villain? What were the rewards for beating it? So many possibilities could've stemmed from it. But for reasons unknown (to the general public, anyway), we have no clue.