Wow, some really interesting suggestions here!
For Uncle Andrew, I'm not sure how I feel about Benedict Cumberbatch. Uncle Andrew supposed to be a bit frightening, and considering Cumberbatch is kind of fangirl material....

I'm not sure how they could pull that off convincingly and stick to the spirit of the book. (Like, there are plenty fangirl-material-villains in movies, but I don't know if the TMN really has that aspect to it.) Cumberbatch would be the star of the film. I kind of feel similarly of Matt Smith.
I am not familiar with Peter Capaldi, but he looks like he could really pull off Uncle Andrew.
Maybe it's just this way for me, but I like seeing someone who is not
too noticeable, especially for the main characters.
The Lady who played Caroline Bingley as LotGK is really convincing! Her poise is very similar to what I pictured of the LotGK. She has the green eyes and everything. My sister just reminded me that she was Mrs. Watson in A Game of Shadows. That's a good reference of the actress not acting intentionally mean, as she was acting pretty sour as Caroline Bingley.
Colin Morgan as Rilian - that's a really good one. I can totally picture that.
I'm still *cough*hopingforLiamNeesonasAslanthoughthatprobablywillnothappen*cough*
I'm familiar with Dev Patel from Slumdog Millionaire. Rabadash... no, I can't see that.

Emeth is much more convincing. If I remember correctly, the actor had a quiet, soft-spoken role in the aforementioned film, so I can really picture him as Emeth. For HHB, I'm thinking that they might collaborate with Bollywood actors/actresses who are less mainstream in the Hindi film industry (like those they picked for Life of Pi).