Cool angle. The part I would stress in the UX is not "make a nicer itinerary" but "make the last mile falsifiable."
For travel plans, the failure cases I see are: (1) a park alert or road closure that invalidates the route, (2) permits/timed entries where AI sounds confident but does not reserve anything, (3) weekly/seasonal closures, (4) place names that resolve to the wrong location, and (5) days that look pretty but require hours of backtracking.
If your tool can show a red/yellow "needs real check" layer next to each stop, that is more trustworthy than a polished AI day plan. I work on a related validator for city itineraries, Tripsapien (https://www.tripsapien.com), and the highest-value signal is always date-specific validation: is this actual place open/bookable on my exact travel dates? For national parks, alerts/permits/weather are the equivalent moat.
