Oh boi Kaiba technically owned dartz in and the pink rose hair guy in the series. Since they are adding non manga characters such as Sartorius, Hassleberry and Chumley I don't really see any reason not to give us Dartz since plenty of people remember him.
Seriously, she at least has more than 3 cards printed, and she has a generic "girl" deck so Konami can throw any "girl" card for her drops/level-up rewards.
Dartz literally has only 3 of his cards printed (Shunoros, Seal, and Geh), and none of them works with each other. And his deck theme means you can't just slap random cards as his drops/level-up rewards.
Seal, Geh and Shunoros are all better cards than any of the cards Serenity used, however.
I don't see what's stopping them from doing Dartz if they really want to. They could go for a snake theme or something if they really wanted him to have a theme, or else just go for cards based on ancient stuff. It's not like cards like Twin-Bow Centaur were heavily Orichalcos-inspired anyway.
im having a difficult time with that :/. im out of +1000 items and my duel world dm is at stage 60 which means i have to face level 57 decks. and the new ones are difficult af. i either have to be patient or hope that i can get a chance if an event happens where he uses a low level deck.