Interesting app. Planning, expenses, and keeping people on track during the trip are some ways I'd think about using the app. TripIt is what we use for the latter. All things get recorded there starting with flights that bookend the trip. That's particularly low friction to get going. You know what you need to fill in next whether it's transport or accommodation.

Your app seems to appeal to the planner type of personality making it too high friction for me. I like to plan trips, but this approach is just way too heavyweight. If I was to suggest an approach that might augment what you have while being structured to an extent (I don't love the shared doc approach) is to allow someone to sketch an itinerary on a map. Then zoom to each general location and do searches for known things to add. Also allow the option to search for general things like restaurants in the vicinity. Bringing in this Google Maps-esque approach would help me.