This sounds like great / amazing 'news'.
But speaking of this 'different rock types', have you thought of investing time just for a few 'nailed to the wall' textures ( like how many can Kelvinr may be able to create, as he wishes ) and unchangeable texture / geometry.And for the rest you can let the user work for them? ( I meant that a few textures should be in order from the engine itself like an example or the samples that Kelvinr is creating.. but a more wide diversity of textures should be created by the user)
I mean... I would love to have the power in my hands to manipulate the shape of the geometry and texture.Like being able to introduce my own set of 3D vector coordinates to change the parameters of the algorithms that you created, and introduce my own photo-shop made textures on top of that geometry.And not needing to hack the files, and probably breaching some kind of legal right from the contract agreement, and instead have a interface for this kind of 'freedom'.
And to give you an example..
For example lets say we have a beach with sand.As you see it... the beach is empty.But you can apply and "invisible road" ( like the current road, but with no texture in it, but instead you will have pre-made objects ), and on that 'invisible road' you can add objects made from 3D coordinates or import a model of a small rock or multiple rocks that you want to mix, because you want on that area to be populated only with that kind of object.And you can set parameters like how many rocks(or pebbles) of that type you want to have per square meter.And those rocks would be converted from the 3D geometry of the model you have imported or the handmade coordinates of the geometry that you applied to the script.And other parameters like the height where the rocks should be placed, the density per square meter / feet of their nature.
You could even place this in the air, like some floating rocks, or asteroid belt ( but there I guess it will be another method, but lets stick 'small' ).Anyway the 'rocks' or material that you apply would be attached in to the geometry and texture like a road, on top of the original terrain.Like if you want to remove 1 rock or dig with a shovel you will hit the original sand texture from underneath, and place the entire geometry of the 'rock' that you shoved out from that spot with the shovel someplace, somewhere near.
Or even remove it for good from the plain of the 'wave' that is embedded in to the original texture ( like the current roads ) trough the 'wave plain'.And put it in your truck and use it for building stuff or making something with them, like a 'natural' dam on a river or before a waterfall or something.And the 'plain' it would be like a 'wave' type 'road' appliance as I said similar to the current road appliance.Only that the 'terrain' geometry from it could be modified not only when in the engine in the 'edit mode', but more likely when stepping with a large truck on those beach rocks they will go deep inside the sand because of the weight of the truck passing over them, and leaving a trail as in reality.
And you could do the same with the current geometry / texture appliances of the roads we have now.Or for example the gravel road to transform it, so that each pebble would have its own thing going on when you pass with a car / truck over it.Plus the movement of the geometry when stepping on them or something like that could have a sound, like in reality.The friction from the 'wave'-like movement when forces applied.Or those 'objects' can be trees rooted in the ground, that you make in some 3D modeling software.. and you can struck them down to the ground with your truck or car, and cut them in to pieces, load them in your vehicle and etc.. ( but this may be a bit off from the 'simple' idea that I started in the beginning of this reply ).
Hope you like the idea if you haven't thought of it yet.And maybe one of the multiple things I said here becomes reality.