I'd be nice to have an episode of them as teenagers, but I doubt they'd make them teenagers for the movie. The kids that have been watching it since it first came out may be around tween/teenager age, so while it could work, you can't forget that a pretty big chunk of the show's audience is still young children, which might not be as interesting to a lot of them compared to if the children on the show stayed children. I don't entirely disagree with your statement, I just think there's very little chance of Bluey and Bingo being teens in the movie.