Katsuhiro Harada, who is the producer of Tekken 8 and the entire franchise of this fighting game, said that in the future in the game may appear characters from add-ons, which will be free for all players.
However, at the current stage, this option Harada excludes. According to the developer, the creation of characters for the game is the most expensive work, and therefore Bandai Namco is unlikely to spend money without potential benefits for their work. But in the future, when Tekken 8 is promoted, perhaps such characters will appear in the game.
Tekken 8 is available on PC and current-gen consoles.