Here's just a quick idea, but Comets could be an interesting new type of body that could be added into the game. Especially if comets are implemented as more than just a new type of simple and static body, but something dynamic and dangerous.
TLDR Below (Cause I write this all in two ways: A short summary. And a big text dump that's as much an explanation of my idea as it is me figuring it all out as I write).
My idea for a comet in DU would be as a transient body that would appear and disappear in game every few weeks or months. Each comet would spawn on the outskirts of the system on a trajectory that will lead them to crash into the sun within a few weeks, give or take. Every comet would be different/procedurally generated, but would basically be like a medium to large asteroid covered in a thick ice and rubble shell. Large boulders, some as big as buildings dot the surface. And caverns up to the size of cities hide within the ice. Beneath which would be a rocky semi-solid core housing deposits of extremely rare and valuable ores. As the comet nears the sun the surface of the comet will begin to slowly vaporize (not physically, so no complex voxel physics) and create two beautiful cometary tails (because that would look incredible in game). Even closer to the sun the comet will begin to 'offgas,' producing a slowly noticeable force on all players and objects on or near it, growing until the force is enough to blow players off the surface as the comet approaches the surface (Basically could function like negative gravity so no complex wind physics. And, is a cheap way to kick people out of and off the comet before it is despawned). Until the comet finally crashes into the sun and those who managed to mine it successfully and survive return to Alioth with their riches.
The main purpose of these comets would be to hold some of, if not the rarest ores in the game. Perhaps they could be the only places to find ores necessary for crafting of FTL engines, Warp-gates, or Fusion/Antimatter Reactors to power them. Rather than just hiding them in a few planets or moons, transient comets would create a game-wide gold rush event as players and orgs race to reach and mine them before they disappear. Not to mention the battles if not all out wars that could result as orgs and nations fight for control of a comet. And the ensuing espionage, smuggling, bribery, backstabbing, and other fun stuff that would occur. Plus they would be harder to camp than asteroid or moons, since they don't last too long and once found it is a race for everyone to reach them.
As for mining, beyond ices and basic ores the main attractor would be said rare ore. These would be buried up to several km deep beneath the ice and rubble, in the core of the comet (maybe the ice could mess with Territory Scanners too, forcing players to mine old school?--Unless that's going too far). To make mining more fun and challenging the interiors and surfaces of comets could be made to change as it nears the sun; adding another layer of danger to staying on one for too long. Geysers erupt at random as the heat begins vaporize the surface. Boulders could be thrown about in the low gravity when this happens, along with any unsuspecting ship or mining outpost. Perhaps pockets of pressurized gases appear, awaiting miners to accidentally uncover them and explore. And, pending voxel physics, the surface itself could shift over time. And finally, extremely rarely (like yearly or less), the core of a comet could survive and create a 'gold rush of gold rushes' as players race to mine the now uncovered core.
All of this is something that would need DU to implement new physics. Particularly either a switch to systems where planets and bodies have proper orbits (like Kerbal Space Program), or at least something to allow mobile comets and small bodies. And the geysers, vapor wind, and etc. would probably need new physics as well. At the very least basic transient comets could probably be done without needing to change much in game. I just really think implementing something like this would be a very fun and interesting addition to DU that would be much more than just adding another type of static body.
Please let me know what you think of my idea, if there's anything I missed, or if you have suggestions for it.
TLDR: Add comets that appear every few weeks or months, on slow crash courses with the sun. These comets would hold extremely rare ores deep beneath their ice shells, that players and orgs would need to race to mine before they are destroyed. Not to mention creating a gold rush and focal point in the game that would cause all sorts of battles, wars, smuggling, etc--as orgs fight for dominance and players try to sneak by and mine the comet. All in a race before it is destroyed. And, pending physics/how far the devs are willing to go, comets could be made dangerous themselves with geysers, shifting surface, and exploding pockets of gas/whatever. Having comets as catalysts for game-wide gold rushes is the main idea. That, and comet tails would look amazing in DU.
Adding on to the ice idea above maybe give players a way to even trigger the event themselves. such as find a massive asteroid with ice thats to thick to mine through, then they have to strap engines onto it and push it toward the sun to start the process.
I love this comet idea and would like to suggest the following:
Ensure most comets appear outside of the safe zone to serve as PVP focal points.
The layers of ice becomes soft enough to mine after certain periods of time, making the comet an event that can last for as long as necessary to allow for different players to participate in the event.
