Personally, I think
Emmara Tandris could be cut. If you don't want to cut her you have space in the Sideboard.
Selesnya Sanctuary slows down tempo a little, being a bounce land and all, so I think you might want something else. Exactly what, I'm not sure... If you like it, you should keep it, though. I would take out Scion weird as it sounds. You're right in that everything in your deck serves a good purpose, so it was difficult for me to make suggestions, but maybe Rys in Sideboard? Seems to me that you have enough fast population capability without him. But he's good, too... especially for exponential
flood... but I'd imagine you'd have won by the time you might be using him, so 've drawing him as a 1-of isn't something I'd rely on... hmm... tough decisions...