Only low-end (what I would call low end anyways, i.e. not professional) screens have gone to 16:9. If apple were to go to 16:9 on the MBP they would have to essentially redesign the whole laptop around it. Otherwise just increase the bezel around top and bottom of the screen. You still see all "pro" monitors using 16:10, and still a lot of laptops other than Apple's. With the exception of 27" monitors, which I believe is really due to the cost to manufacture them since they're so few.
1680x1050 is better than 1920x1080 IMO. I think you'll notice more screen real-estate with 16:10 vs 16:9, regardless of resolution. I would anyways, but a majority of apps I use have toolbars along the horizontal part of the screen and I use split screen a lot.
For designing I love using 1680x1050 but for watching movies/videos I definitely prefer 16:9 (1920x1080); therefore having said that, I think I would prefer the new Macbook Pro's to have 16:10 screens.