>>/1662/
> how did it get started? Was it just 4cuck shitposting it into a meme than the show embracing the meme and putting scattered anime references and some deeper themes at times? That is both stupid and hilarious.
it is indeed stupid and hilarious. The way to sum it up and that everyone uses to describe this process gets reduced to this one: autism. 

Yep, we use it to put things simple and not trying to explain how this has happened all the time. 
It´s somewhat complicated to describe it shortly but it went like this:
> /co/ hears about MLP
> they expect its release and they are ready to laugh at it
> they surprisingly like it
> they circlejerk constantly about it 
> hype it up with very frequent threads
From here, everything goes like a typical show that has some hype and has found a little niche but:
> /b/ finds it
> decides to shitpost EVERYWHERE and flood the board with ponies. 
> shit goes insane 
> Moot decides to ban ponies after constant shitshows and complaints
> USER WAS BANNED FOR THIS POST every time a pony appeared
> fans of it decide to create sites like Ponychan or alternative places to discuss it and protest about their ban
> the noise was so huge that Moot decides to create /mlp/ and enforce the famous Global Rule 15 in order to keep ponies in that board
> all chan activity for ponies has been focused on that place until /trash/ and /mlpol/ happened, making ponies a taboo for the site in general.

There are a lot of wikis and sites that describe the events much better than this. It went much further than even her own creator would have expected. That same creator (Lauren Faust) visited /mlp/ in 2013 and there was a huge bomb of shitposts and drama not only for that visit but for the franchise in general. 
All in all, nothing has been expected, just a wild ride with a wide range of emotions.