-1) is there any way to bring back in Houdini some sort of class attribute or tag from actors in UE?
-2) is there any way to populate the input node dynamically? You throw some rays, and you feed automatically into the input the actors they intersect.

A practical application would be to create procedural trees that react better to the surrounding objects, and not only the simple landscape. For example, there's a house nearby, or a big rock that the roots should avoid to grow on, another specie of tree in competition… etc

Only thing I can think of:

Every object in the scene register its position and its class (tree, rocks, fence etc) down to a .csv file, which is then read by the digital asset placed in the scene. Positions are calculated and items within a certain radius (from the hda) are loaded into the hda from the disk, and they can now undergo any collision detection..

Sounds complicated, but maybe there's a better and simpler solution?
I'm not expert with Unreal…

Hey Andr, I don't think there is one right solution. Every project is different. While using Houdini Engine on a slightly bigger scale you need to rethink your pipeline and do some work around it.

It all depends on what you would like to achieve. You could also build your scene in Houdini by placing all assets directly Houdini. Then you can save their transforms, model paths, whatever to CSV, and recreate that scene in Unreal.

Are you using Unreal just for Rendering or it's a game? How much of Unreal needs to be used to level/map/scene building?

Version 2 of the plugin has updated world inputs:
When in bound selector mode, selecting an actor will send to Houdini all the actors/components that the plugin can translate to Houdini.
There is also an option to automatically update bound selectors, so that adding new actors in their bounds will automatically update the houdini input, and potentially, trigger an update of the HDA.