Thanks, Yo! I'm having a blast working on it. Do you have any insights on how to make the interaction between the players more interesting?
ooh good question.
at first glance what seems to be your biggest challenge is that the world is super big and the concurrent players are not. The festivals are a good way to do that.
I suppose to encourage interaction social tools are always good, though hard to moderate. id say maybe have a possible LED display on the balloons or releasing party balloons with emojis.
I'd suggest you play Sky:children of the light for inspiration if you havent, they do really great UX around multiplayer chill experiences. For instance I'm thinking you could have a group system where a player can lead a bunch of others. Or maybe just make wind around them. That works well in the "lean-back" experience.
Of course my personal itch is to explore, but thats a pretty different thing and maybe you want to stick to areas where google has 3d models. However this does bring to mind the whole "driving simulation" genre with social phenomena like truckersFM (maybe reach out to them they might dig a partnership). I don't know much about this genre, except that its big in Germany XD But there's an audience for it, I think the game "the long drive" is quite popular.
If you wanna go that way you could just spawn a treasure somewhere on the map, could even turn into a race. And then you can go the whole "scavenger-hunt"/"around the world in 80 days" route xD
Oh and steampunk themed balloons of course.