I think there will be a new playable character in TAK soon.
The reason for this (or rather, this is just my speculation) is that other Apple Arcade games have actually added new characters and stories that fit those characters in their updates. For example, Puyo Puyo Puzzle Pop has added several characters and their stories in its updates. In Sonic Dream Team, it was recently revealed in Sonic Central that Shadow will be added, so it's likely that a story exclusive to Shadow will also be added.
And if a character is added, who will it be? It goes without saying that it will be Melodytchi. It would be strange to have her not be there when there is Lovelitchi and her younger brother, Kuromametchi, and she (probably) doesn't even appear in TAD. However, looking at this from the other side, it means that there is a possibility that she will be added as a playable character in the future.