Well here's my take on that:
Rant incoming!
You know, i think the biggest reason for the success of the manga were neither the characters nor the plot. Rather it was the world. Either knowingly or unknowingly he created a world that was nearly on par with the likes of 'Song of Ice and Fire', 'Star Wars' or 'Lord of the Rings' if not a bit contentless. But it had and has so much potential, the fanfiction is proof enough, to much, much more than even Kishimoto could have drawn with a thousand chapters.
Demons like kitsune, tengu or tsuchigumo, Daimyos and politics, vast chakraless armies of commoners led by chakrawielding samurai, cultural differences and similarities, horrors like human experiments and mutants, old repurposed legends (sannin), small ninja villages of foreign custom with strange techniques, vast unknown lands and countries, villains with different motives, and the list goes on and on.
And that's the tragedy Kishimoto caused, in making villains 'twisted but good' people, shying away from letting real humans fight to death (4th ninja world war), leaving the romance out to shrivel, introducing one-dimensional characters and not giving them development (Hinata) and many more (Sakura and Sasuke's development retconned) he stiffled the fandoms creative spirit and forced it into always the same routine (following canon) because the chapters after pain were less about the world as about a select few characters he made unnaturaly overpowered (Hashirama, Madara, Naruto, Sasuke, Kaguya). So instead of stories like 'Will of Foxfire' from Quill of Moliemon we always get identical fics about a neglected Naruto getting together with either a harem of older women (with incest of course) or with Hinata, instead of truly original fics like those of Case13 we get canon retelling no.40 and in place of openmindness of characters we have sensless hate thanks to an inept at character writing at the drawing board.
Instead of fully coloring the vast canvas he had of the world called 'Naruto', he painted those parts he needed for his story and build a rollercoaster, always following the same route only with a few twists and turns that fanfic writers are very hard pushed to break out from. And with the destruction of his plot and characters (the railroads and the vehicle if you will) he has a very good chance to let his fascinating world slink back into obscurity.
That dumbass should've concentrated on fleshing his world fully out instead of speeding ahead with one story in a possibly gigantic and amazing world , not caring what he leaves behind...for true fans to pick up.