A release date hasn’t yet been announced, but Bandai Namco has said it’ll be out before April next year.
In total, six unannounced characters are mentioned- Shaheen, Raven, Zafina, Yoshimitsu, Steve Fox, and Alisa Bosconovitch.
Bandai Namco has said that Tekken 8 is set to have a much bigger at launch than its predecessor did, and many of the characters that will populate that roster have already been unveiled.
Whether are not these are all the unannounced characters that Tekken 8 will be confirming before its launch or just a selection of them remains to be seen.