WTH can't I populate a group with entities from an area?

I like to toggle the lights in an area, but using the behaviour that toggling a group has.

Toggle all lights in an area: Flips the state of all the individual entities
Toggle all lights in a group: Flips the state of the group as a whole

It would be so nice to have a group helper that, in addition to assigning individual entities, could also add entities by area and label (perhaps device too). The group should auto-update on changes to area/labels.