Under consideration are currently the Bard, the Monk and various other candidates such as the Psion. But each of those additional classes comes with some drawback, e.g. the Monk would require a lot of high quality martial combat animations , the Bard has some redundancies, etc.
For now, firstly and foremostly, we need to complete and polish the eight base classes and the related prestige classes. Especially the Rogue has some massive features, such as stealth and lockpicking, that require a lot of attention and development efforts.
So, right now, we can't promise any additional class on top of those eight for the first release of the game. But since we plan to evolve this game over the next 10 or so years, I am sure at some point, we will see new character classes - implemented by us or by other users (our RPG framework will allow that).