It'd be nice to have basic waypoint functionality, especially on a $600 GPS device.
Nothing too fancy, just the ability to add basic icons in Garmin Connect for things like stores/restaurants, mountain tops and when you're out on long rides in the mountains, camp grounds so you can fill up the water bottles and for the many folks that do organised rides, brevets, randonnees, rest stops. Have an extra field on the Edge that allows you to show distance to the next waypoint.
Seems ironic that I still have to rely on a piece of white masking tape on the top tube with important locations and distances marked in a Sharpie, pretty defeats the purpose of buying the 810 in the first place.