With 1.9 fully out the door, work has already begun on version 1.10! So far, the first (and only known) teaser to the new content is talk of a new creature in the game, mentioned in a tweet by Jeb not long ago. Other than mentioning the base color ("242, 242, 242", an RGB code for an extremely light, nearly-white grey color), not much has been said about it.
In the meantime, 1.9 is already being heavily tested by mappers, modders, and resource pack makers far and wide. Don't forget, you can catch up on all the crazy changes in 1.9 over on the official Minecraft wiki, which also has an official app, letting you read up on all things Minecraft no matter where you go!