The Hasbro product numbers for the four that were revealed, is missing a number... so it's possible there are more to come (or there were more planned), as it would be annoying not to have the full set of Autobots and Decepticons... and they could keep going too, with the Horrorcons (Apeface and Snapdragon).

Chromedome: Hasbro product code # F1022
Hardhead: Hasbro product code # F1023
Brainstorm: Hasbro product code # F1025
Mindwipe: Hasbro product code # F1026