Given Clayface is dead (last I checked not sure if that still stands) I think it'd be cool to have Ethan Bennett from The Batman series appear and become the new Clayface. I enjoyed his dynamic with Batman/Bruce especially given he and Yin were often at odds wondering if they could trust him. I figure it'd be good to see Gordon get fired from the GCPD and for Batman and the other vigilantes to be against the GCPD headed by a new corrupt Commissioner. I like idea of Ethan and Yin being one of the two last honest cops left.
I also like the idea of Twoface becoming a more active threat and playing a key role in Ethan's story maybe even telling Ethan he can't trust Batman and when Ethan has his one bad day he begins to feel like Twoface was right. As for Ethan's motives I can see him having a grudge against corrupt officials and attempt to impersonate them claiming to be fixing Gotham in his own way. I also like the idea of him discovering Bruce is Batman during his mutation and for the revelation to contribute to his mental decline causing him to see Bruce as a liar and accuse him of betraying/deceiving him.
I think that'd cause a lot of tension for Bruce and I like the idea of Ethan being paranoid about trust and reflecting that aspect of Batman just as his other rogues are like twisted versions of himself. I also like the idea of Yin helping Bruce reinstate Gordon while working against the corrupt police.