Ok, calling this one done for now. Not super happy about the background, but I don’t dislike it so “good enough”.
This was mainly a test of Hesiod, an open source node based terrain generation tool which is still in its early days but works quite well (small artifacts aside).
Also, I saw a wallpaper like this but it was unfortunately slop, so I thought I’d have a go at re-creating it using “classic” 
procedural generation.
The end result was more inspired by 70s airbrushed sci-fi art and it was fun to go for an effect like that. The scene is rendered in Eevee without raytracing and with no lights. 
I also used standard color management since I found that to give me greater control over the exact colors I wanted.
Wireframe of the scene.
Screenshot from Hesiod.
Materials for the mountains, just a directional mask with a gradient.
I created a little geo nodes tool to tune the mountains shapes
The final scene patched together (fog hides all crimes)…
Each empty sphere in the above screenshot is one of those geo node modifiers I created to tune the shape of the mountains, but I also used them to flatten the sides to get that abstract feel… happy accident, I must confess! 
