What was Eren's vision about?
I agree with @Maroon. It's basically just a foreshadowing dream/bad feeling he had which combined his existing knowledge with his aspirations/dreams.  

However he does have legitimate flashbacks/dreams he doesn't know anything about later in the show/manga and discovering what it all means is part of the plot. He also keeps dreaming about a "female" he doesn't know.  His memory is hazy, and there are 


   the lost 3 years when his father experimented on him 


which I feel they will reveal over time. He also probably has memories/dream issues associated with 


   being the controller 


though it wasn't revealed if he became that 


   during the 3 year break or was like that before,


which could impact whether his dreams were induced by or related to it.