The whole 'This is, ah, my castle' line Eddie states directly coincides with Chrissy being 'Queen (of Hawkins High)'. He was basically referring to himself as a 'King' and therefore her equal. I get Eddie was not a shy guy, but he was laying it out there on the line to his crush and that's pretty brave thing to do without knowing how the other feels.
The very fact he is referencing himself as her equal at that point really makes me want to know what was said in that van!!
Also, the way Chrissy is smiling as she leaves the van, it's canon there was mutually acknowledged attraction at that point.
This is why I believe they are coming back... I don't think Duffer's would let a romance like this just pass them by. Grace and Joe's poker faces in Canada as well about them being 'dead/gone' now was a giveaway I think...they know something we don't!
There is no way have seen the last of Eddie and Chrissy! Personally, I am expecting a full endgame. I just don't know if it will happen in ST5 or a spinoff....
