I hadn't heard this. I've heard over the years rumours of proposed episodes, but they've never materialised.
It'd be strange without Hugh Laurie as George. He became as likeable as Baldrick's spelling. However, yes, with his success in "House" it would be pretty difficult for him to reprise his role.
I didn't know Stephen Fry was busy with other things, but if he is, then its understandable that he wouldn't be able to participate.
What about Tim McInnery and Miranda Richardson? I mean, Percy was a key character in two of the series, and Miranda Richardson was vital to the second series. I'm sure there's other characters who appeared in a number of episodes but I cant think of any of them yet.
It would be good to see a new series - there are so many historic events the writers could choose from, and I'm sure there's an audience for the show. The big question remains if and when will it materialise?