Great news? You mean ridiculousness! Snape's physical appearance is a huge part of his characterization. If this man is indeed cast, you might as well make up a new name for him because he looks nothing like Snape is supposed to! This is in no way directed at the actor himself. He could be the most talented actor in the world (and maybe he is, I am not familiar with his work) but that's not the point. The point is that Snape has pale skin, greasy black hair, and a hooked nose and unless I'm blind, a handsome young black man does not fit that description.

If HBO wants to incorporate more diversity, choose another character whose physical description isn't so specific. i.e. Other Gryffindor students, Quidditch players, Ministry of Magic officials, etc. There are plenty of opportunities to hire a diverse cast without completely ruining the show.

I also find this casting approach to be very patronizing towards the minorities the network is trying to include. These big networks are trying to be more diverse but are completely going about it the wrong way. They seem to think that casting POC in major roles is what the audience wants to see, irrespective of whether the character's appearance is important to the role or not. This ends up having the exact opposite effect of what they're expecting. And unfortunately the actor often takes as much heat from the public as studio execs when they are just doing their job. My gosh, write new roles for POC that are just as important as any other character but that actually match their physical descriptions! Or if they decide to cast someone of a different race or gender in an existing role, at least go with a character whose appearance isn't mentioned or isn't important to the storyline. That will give the actor the flexibility to make the role his or her own and actually be recognized for their talents.