There are a few unreleased heroes that have been found within the game files. Some of them have all of their skills and SI items, while others only have a story.
Keep in mind that the unconfirmed heroes might not ever be released or could be completely redesigned in the future.
Based on the level cap found within the game files there is likely to be at minimum another 9 new heroes planned for release.
Izold – The Forgotten Champion (Graveborn)
Tidus – Shadowmane (Mauler)
Cecilia – Purger of Sins (Lightbearer)
Solise – The Floral Wonder (Wilder)