According to the5krunner, Garmin is going to introduce a few new features specifically targeted at ultramarathon planning and racing. All of the new features seem to revolve around course points - this is what Garmin calls on-route waypoints:
Cutoff Times: Add specific cutoff times to course points, triggering countdown timers on the watch.
Rest Breaks: Insert scheduled rest stops with durations at specific course points.
Course Point Notes: Add custom notes to course points for strategy reminders or aid station information.
Multi-Crossing Support: Choose specific course points when a course crosses the same location multiple times.
Bulk Management: Easily delete all cutoff times, notes, or rest breaks from a course.
For me, the most interesting and helpful are features #1, #4, and perhaps #2 and #3.
While I am never at risk of chasing cutoff times (not yet!), attaching times to waypoints would be a good way to race against a previous run on the same race course. I sometimes write down splits to aid stations on a piece of paper and laminate it, or even use my smartphone, and then try to chase and beat those splits.
The multi-crossing support is also very important, and I have commented on that in both Garmin and Suunto forums. In fact, if I try to add a waypoint on an out-and-back route in Suunto App, there is no control on whether that waypoint is added on the out path or on the back path. I did an experiment recently and it seemed random. But in practice it is very common in many races to have aid stations that are visited multiple times at different distances during the race.
Turning a race timer automatically when reaching a waypoint is also an interesting feature, however it would rely on the waypoint position being accurate, which isn’t always possible when planning a route for a race. Having waypoint notes might be interesting too, however I can’t imagine reading that from a watch screen. Maybe.
But in general, any ultramarathon specific feature is always a welcome addition!