The pre-order page for Tekken 7 went up on the Japanese PlayStation Store and it gave us a few more details on what will be included in the Season Pass of the game.
Avoiding The Puddle has translated the details and it sounds like some guest characters will be added to Tekken 7. This is in addition to Akuma already being included in the launch roster.
Anyway, the first DLC pack for the game is planned to be out in Summer 2017. A new game mode will be added plus 50 new costumes will be added for characters to wear.
The second DLC pack will be out in Winter 2017 and it will include a new guest character. The guest character will also have a stage and costumes as well.
Finally the third DLC pack is planned for early 2018 and will include a second guest character. This guest character also has a stage and costumes. It is possible they are more Street Fighter characters?