While still experimenting with the new End, I created the clay Creeper face to summon a second Dragon, and then when I killed the new Dragon it summoned a new Exit Portal and a new Gateway

To Reproduce:
1. Go to the End and kill the Dragon
2. Either create a clay Creeper face on the ground or type "/summon EnderDragon"
3. Kill the new Dragon
4. Watch for new portal and new gateway