So one of my goals to start with was data autonomy. Campaign-planning and worldbuilding is really personal, so I wanted to find a way for users to feel in control of their data, while still having robust online features. Implementing a hybrid CRDT application is really hard, it turns out! Especially when your users are super prolific. So building an offline-capable system, able to gracefully support collaboration, that would still scale to thousands of docs, has been the hardest part. I think fundamentally we accomplished that goal, but there's still lots of improvements I want to make.
Another hurdle that fellow developers might be familiar with is dealing with IndexedDB across many platforms... Including Safari.