The preorder information for Tekken 7 has shown up on the Japanese PlayStation Network, and Bandai Namco's plans for the game include two fighters from outside the world of Tekken.
The first, coming in summer 2017, will feature a new game mode and more than 50 costumes being added to the game. A second will arrive in winter 2017 with the first "guest" character, along with a stage and costumes for that character. The third DLC pack will arrive in early 2018 and offer a second guest fighter along with stage and costumes.
Bandai Namco has added guest characters to its fighting games before—Gon appeared in the console version of Tekken 3, and the SoulCalibur series has had many cameos—but it remains to be seen how outside characters will be integrated into the Tekken 7 experience.