Season 2 is going to be focused on the Cluster and it being the big big bad.

Season 3 will probably be about Homeworld and possible a second war.

Here's how I see it, 

Season 2a-fusion, the Cluster is the big bad the group has to beat.

Season 2b-basically this will give a little more development plus it will tie up a few lose ends, after this we're introduced to the true big bad.

Season 3a-The history of the gem war, a little more on the background of everything, it'll also tie up a few more lose ends.

Season 3b-A second gem war, unless we get further confirmation season three may be the last one.

Season 2b- The Gems doing absolutely nothing about the Cluster

Season 3- Pingas

Season 3b - Stevens sacrifice

I made a 3 season opening! but i can't show you (i don't have a phone)

it begin like this:

eveyone is black

so the light opens and they summons their weapons saying we are the crystal...

so steven and connie appears and says gems

everyone in the portal like a circle

then appears Jasper and Garnet summoning their weapons, then Pearl and Peridot, then Lapis and Pearl and finally Steven and Connie

they run to defeat a gem monster

and when they attack the monster they say their names

We are the Crystal Gems! Jasper, Garnet, Amethyst, Peridot, Lapis Lazuli, and Pearl! And Steven and Connie!

We.. Are the Crystal Gems! Created from Homeworld or not, we always save the day, and don't doubt that because we'll always find a way! And that's why the people of our world believe in: Garnet, Jasper, Amethyst, Peridot, Lapis Lazuli, and Pearl! And Steven and Connie!