I would also love lava caves, from what we know they should be much more common than their current non-existent state and some of them can be quite large and winding, perfect for racing.
I would also like to see large fissures, ravines, and cracks. There are canyons in-game but I think they could be improved a lot, they currently look like the sort of "canyons" you could make in one of those last-last gen games like Fracture or that you could find on planets in Mass Effect 1. No sharp edges, overlaps, high-frequency details etc. All should be really common in an environment without erosion.
I'm really excited for the future of this game. Clearly the developer is passionate about it, and they seem to have some impressive technical chops to achieve these things. I think exploring the galaxy just for the sake of seeing new sights would be much more appealing if there was a realistic level of interesting landscapes on planets to find and explore, even if they were implemented before atmospherics.
But who knows, maybe they don't want to update the Stellar Forge (or planetary generation if that's a different system) all the time so they don't ruin CMDRs finding interesting things in the current system. Maybe they want to wait for one big update so everyone can take it on the chin at once and afterwards have much better planets across the board. I don't know if that fits with how they're developing though.