We've had several requests for adding diplomacy. Right now there are other features that we want to prioritise first. However, we have this in our backlog, as well as trading/sending resources, and features that are mentioned get bumped up in our backlog, so thanks for commenting on this.
We're definitely going to add river mechanics at some point, with fishing and boats.
It's fine to post your suggestions here! You can also send them on Discord.