Hi Mark
1. Terrain painting is half done, its quite complicated to do, so it might take a while
2. That would come with terrain painting
3. I dont think so, i tried but i run into permissions issues on non administrator running users
4. will come with no 1, for now you can just crop the image id imagine
5. You can use OBS or Shadowplay to record an animation
6. Ahh the all elusive water simulation, im not even sure where to start with that one, i use water sim in my VFX job, and they take hours to simulate.
7. Adding more skyboxes in the future
To be clear, this app was made with the intention of allowing ordinary people be able to paint some nice images without knowing the technical aspects of 3d modeling apps. All of your suggestion + more can be done with blender, 3ds Max or Maya. I am not trying to compete on features with these packages as they have a team of dozens working on them, perhaps you could download one and see how you go. Initial learning curve is high, but you can do so many cool things with them that you will never be able to do with flowscape. I will always try and update it, but it will always be focused around simplicity rather than complexity.
hope that helps
cheers