Looks like Terrain Tools will be coming officially in 2021.2

From the a15 release notes, among others:

• Terrain: Changed: TerrainAPI namespace is no longer part of an experimental namespace and has been renamed TerrainTools.

• Terrain: Changed: TerrainUtility moved to UnityEngine.TerrainUtils namespace.
  
  
• Terrain: Changed: TerrainUtility.TerrainMap moved to UnityEditor.TerrainUtils.TerrainMap. TerrainMap.TileCoord moved to UnityEditor.TerrainUtils.TerrainTileCoord.
  
  
• Terrain: Changed: UnityEditor.TerrainAPI.TerrainPaintUtilityEditor.BrushPreview changed to UnityEditor.TerrainTools.TerrainBrushPreviewMode.

Excitement!

 

This info about Terrain SRP Details might be also interesting:



I hope there'll be a lot more samples, not just grass

 

I am really interested with terrain tools also. I really wonder what is comming next with terrain tools 4.0 and when...

 

For the interested ones: 2021.2.0a17 imports a pre version of Terrain Tools 4:



Change log:

https://docs.unity3d.com/Packages/com.unity.terrain-tools@4.0/changelog/CHANGELOG.html

SpeedTree 8 support is also in for HDRP

 

Personal comment on that release: Looks like they made it only release ready and labeled it 4. The Bridge Tool for example is still pretty much useless. And you still can't combine texture painting with the other brushes.