Arthur and the gang have been in third grade for sixteen years now, among other things... if there were any differences or advances that could be made, what would you like to see?
Personally, one thing I would like to see is considering D.W. turned five in one episode, and Emily mentioned she'd be going to kindergarten, I'd like to see D.W. actually in kindergarten, if only because I think that would make for some really interesting tension at Lakewood Elementary; just yesterday, the episode "D.W., Dancing Queen" was on, where the preschool class was at Lakewood for the annual third grade/preschool partner project, and we see D.W. go out of her way to embarrass Arthur by mentioning his underwear obsession to her classmates. I can see D.W. doing that very often, just to irritate him, since that's what little sisters are supposed to do... of course, we could also end up with some other interesting scenarios, in the event that say someone is picking on D.W. for whatever reason, and if Arthur sees this, suddenly his big brother instinct kicks in and he tries to get the bully to stop picking on her.
I don't know.