when will we be able to fully modify and customize the world generation with new plant life, random sticks and stones and add more detail without it being static?
Basically this is possible through the plugin API, but these elements need to be placed "manually" by the plugin.
After this update can you please consider some other options to help the modding community out? Perhaps someone in there could even solve the riddle of flowing water
Adding something like dynamic water isn't possible through the plugin API unfortunately. Basically the API is just a way to allow people to create mods easily, but the API isn't the same as "classic mods". The API contains a bunch of functions and events, and we're implementing the actual behaviour "under the hood". For example, if you want to add a new model through the API, you just have to call a few methods for that, but "under the hood", there is a lot more stuff going on (maintaining the model information on the server and client, handle the file download, handle the rendering on the client, handle the client interaction with the model and sync it with the server etc). As a result, there are always some "limitations" to the API - you can only access the functions and events which are available in the API (by using reflection, you could get some more access, but since plugins always run serverside, you cannot modify the client that way). Usually we're always listening if someone requests a new API feature/event (unless it's too complicated to implement) 
However, of course it's still possible to create "classic mods" by modifying the game files (i.e. the same way mods were created for Minecraft in the old days). This gives full freedom and you can literally change everything, but this is much more complicated than working with the API of course.
In a nutshell, it's still possible to create classic mods with the ability to change everything and turn RW into a completely new game, but the API is much easier to use and more convenient (since plugins are always running "server side", the client does not have to install the plugin when joining a "modified" server), but also more limited 
We're mainly focusing on NPCs (i.e. bandits, skeletons, but also reworking the current animal AI and collision detection), but as @Captian_Cornball mentioned, we're also adding more functions to the API (for example, we're going to provide an easy way to add custom items to the game). And of course there will be a lot of other changes and a bunch of bugfixes 