After our meeting, and seeing the sketch in the earlier Answer, I'm ready to share my analysis. Thanks DaaaahWhoosh, not because I like it ☹ but because it served as a strawman to crystalize my vague handwavy ideas.
My reaction: the “planet” (or planemo, large moon, megastructure?) is indeed iconic of meaning “world”, and echos the main site logo.
But what do dragons have to do with anything? Are there dragons in many questions (no) or are they symbolic of something strongly tied to the site (no)? And what are they doing there? Orbiting? Or is this some nations’s flag? It’s not applicable to the vast majority of Qs here and doesn’t evoke a central theme that applies to us.
As a digression, let me point out this Ted talk Why city flags may be the worst-designed thing you've never noticed on principles of good (and bad) flag design. I suggest that this is applicable to the logo as well.
Now let me cover ideas of the larger piece first — what we are calling the banner or page art.
This is not so constrained in size but can have substantially more detail. This is going somewhere so bear with me and I’ll come back to the icon later.
For now, same idea of making imagery that evokes the worldbuilding ideas but not so constrained by size and resolution. This isolates the different issues of design.
I submit that Worldbuilding is not just about geology and geography. It’s about biochemestry, different ecosystems, society, technology; all the big stuff behind the setting of a story. And what makes the stuff different from a normal story is that it’s alien. That is, very different from what we know in real life. It might be far future or alternate timeline humans, but an “alien” society from our point of view. It’s different so it needs figuring out. That’s the step of worldbuilding we focus on here on the main site.
So let me throw out another strawman idea.
Start with a world but not necessarily a normal planet. Maybe a wierd planet or a space habitat. This is iconic for “world” as noted earlier.
Surround it with a few alien beings. Very alien, such as something with tenticles (Ctuluian?) and someone insectoid, maybe a mechanical robot-like creature from the 1950’s, etc. This, clearly, represents the alien aspect. Different biology, different ecosystem, society, etc. just by virtue of being nonhuman and as different and diverse as possible.
Now this scene is a tableau. The group of beings is grouped around what, a model, poster, or map of the “world” (habitat)? There can be other elements in the background or elsewhere, but look what we have thus far:
What are they doing? What is this scene? It immediately suggests some kind of storytelling. Maybe they are forming a peace treaty. Maybe they are preparing to forge a mixed society, or going off on an expidition. (Babalon 5, Ringworld, and other classic stories come to mind.)
The juxtiposition and presentation of the other iconic ideas should itself lead to the larger concept of society, civilizations; and suggest a story is happening here.
Think about the classic covers of sci-fi magazines. Whether taken from the lead story or just an issue theme or cool painting the editor liked, the tableau is evocotive that a story is happening here.
A banner or extended page art can taper off with images taken from many different famous questions and themes explored on the site. Fitting in more clutter should be a different journey for the viewer, more of an Easter egg hunt, and be separate from the thematic presentation of the main elements.
Now let me return to the small icon.
After having viewed and understood the symbolism of the larger piece, the small piece, like Roman Mars’s flags, should draw elements from that but be simple. It should remind you of the main art, and the main art provides meaning to the elements appearing in the small piece. The small piece does not have to define the symbols, but meerly use them as defined in the main picture.
One main element from the scene that is distinct and still iconic overall (once you know the context) is enough. If the aliens are gathered around a (picture/map/illustration) of a distinctive habitat, than that habitat would be it. Think of how the star ship Enterprise is not like any other ship but distinct to the franchise. A blob with indistinct landmasses is not distinct and iconic.
That’s why I speculate on a strange world instead, like a taurus! Imagine a taurus-world with continents drawn out like a political globe. The insect and the ctuluian are gestering with tenticles and antennae to different regions on the (er?) globe.
Story: are they invading? Exploring? Building?
Now the small piece of art can be a close up of the taurus-globe, lost detail but now we know what it is and it has enough color patches in the same arrangements to recognise. Present that as a close-up showing the appendages over it. Or, re-compose the shot but it’s still a tenticle and insectoid antenna (grabbing? Fighting over? Admiring?) the map of the taurus-world.
That tells a story even without the main picture, if the resolution is high enough.
And that’s my idea. But more importantly, it’s a meta-idea of how the art should be understood, regardless of what elements are eventually used.