Personally, I think that if Damian must not go for an original mantle he should become the next Nightwing since his history is about how blood does not tie him to a future, how he does not have to be like Bruce because he can be better (and we all know what being better than Batman means on DC rules) like... it all ties well with Damian becoming Nightwing, Damian is the one true inheritor of the Robin mantle since he is the the Robin of Dick's Batman, the Robin that he gave the mantle willingly and the Robin Dick trained, it is also super cute when people make fanart of Nightwing Damian and they make Damian's color turquoise since it is the middle point of his green and Dick's blue.