This sounds like a strange choice for the DC Universe, and I mean that in a good way. After so many superhero movies, getting a full horror movie about Clayface is much more interesting to me than another hero fighting another villain.
I especially like the Hollywood actor angle. Clayface being Matt Hagen means the story can connect his powers directly to acting. He can change his face, body, voice, and probably his entire appearance. That could create some creepy scenes where people are not sure who they are talking to.