Seems like a no-brainer. Figure out how to make it do something the handheld, laser, and smartphone apps can't do and you'll really have something. Think something like painting elevation lines on the horizon, or superimposing a target. Sure, that'd be against the rules, for now, but would hop off the shelves.
Short of that, the kinds of things GolfLogix does, like yardages and clubs (based on input or history), based on distance to green or hazards would be cool.
If you could really nail the use case for efficiently using them, what to present at different points in a round/hole, that might really take off. What can you do for which you can get IP Protection?