^ Well going by the story line with Paul, I think Chimchar has some importance and more incentive to evolve. And like you said, the interview said that the writers would like to keep the starters as long as possible but Mr. Hidaka also said that pokemon evolve when there are big things coming up. And I think Infernape vs. Paul would be pretty big considering it would be a transformation for little Chimchar to become a powerful warrior (literally). There's a good chance for an evolution but it's just "when".
And I still think it wouldn't be rushing considering Dawn also has 3 more contests to go (and about 1-2 more contests to lose).
Look I'm done talking about Chimchar evolving...while you want it to evolve as soon as possible, I'm giving the writers a bit of time.
Now on to Dawn and Brock.
Piplup = Pikachu basically so I don't think it will evolve.
Pachirisu - no evos
Ambipom - done
Buneary - I could see it evolving since it seemed to look up to Lopunny (I wouldn't mind either way since I find Buneary a cute match for Pikachu haha)
Swinub - It's going to be a while before evolution...Piloswine in Snowpoint and Mamoswine in a probable BF?
Croagunk - I find it too iconic to evolve imo
Sudowoodo - done
Happiny - I'm not sure with this one, I'd like it to evolve but I could still see it as a Happiny if the writers want Brock to have a baby like pokemon.