It’s just for the trailer, we’ve gotten no indication that stuff like that will be put in the game.
Some people have tossed around the idea that Gargos might have unique voice quips for each fighter, which would be cool, but even doing that for 1 character probably won’t happen
Maybe custom lines is something they’re planning for paid DLC. In my interview with Adam back in early January this is something we discussed which is that if the community wants it they may sell them. Also keep in mind that Season 3 Ultra Edtion of the games comes with a ton of bonus KI Gold which MS has hinted that can be used to buy unannounced things coming later in the season.