I'm surprised that it's the BBC that's producing it, I was expecting it to be Sky again. Not that that's a bad thing, if anything I'm more interested in seeing what they'll do with it.
I'm not sure what to think about Rihanna taking over the Discworld. As ITL
said, the narration is a huge part of the series and that's all Terry. She may end up being very good at it, but I'm hopeful that Terry still has a few novels left in him yet and, more importantly, he's able to get them out.