I had suggested some of this before, and I LOVE your nova idea. Maybe even an evil tech that allows nova causing weapons, rendering entire systems uninhabitable. But maybe it is so big of a weapon you need to own a planet in the system to use it. (Maybe allow planetary shields too...come to think of it, that would be cool anyway. Shut down all production + planet growth on a planet, and spend X bc per turn to run shield, but planet and ships in orbit are untouchable, big idea here)
meteor showers, radiation damage from nebula, comets, random event of asteroid impact on planet (or new moon!), solar flares, waking an ancient robot dreadnaught that runs amok all over the map and you have to hunt it down, SOOO much can be done with this
Also, this makes starbase placement even more strategic and useful (kind of like space tile bonuses). An economic starbase might do well in a high energy area with the right module (high energy radiation collectors allow increased production) but would inhibit military and influence starbase due to increased communication interference and dangerous conditions. Likewise, an influence starbase next to a nebula or Van Allen belt or something would attract more tourists, and in empty space it would have increased effect range due to easy broadcasting. Military starbases would benefit from asteroid fields (increased defense from the difficulty of enemy fleets not being able to navigate and maneuver as well, while local ships would have been able to map the trajectories of the asteroids and avoid them) as well as putting remote weapons and sensors on asteroids. Also, military starbases inside solar systems could gain additional advantages as well, due to increased remote sensor placement options.
Whole fleet obliteration events would be great, because it would increase the underused survey ship tech's use. For example, a fleet with a survey ship in it would "see" the incoming radiation or the solar instability and could avoid it, while another fleet wouldn’t have the advanced sensors and analysis computers.
Would also love to gravity related weapons tech, as well as more nanotech and biotech related stuff.
Also, what about water planet colonization? Floating cities on gas giants? These would be awesome as starting bonuses, would help ease the "habitable planet rush" at the start of games, and make an "expansionist" civ choice a really cool option (plus beefing up the relatively small planetary improvement tech line)
Worm holes already exist in game, but what I think would be really cool would be the addition of the historically mentioned "star gates" as a really expensive project that allows instantaneous transport between gates.
Another cool space idea would be finding bonus techs (cannot be researched) in alien derelicts, and being able to find and salvage unique and powerful ships to add to your fleets (but you can't replicate them).
I would also love to additional minor races, and maybe a completely space bound race like the bentusi from homeworld or the roamers from "the saga of seven suns).
P.S. Stardock, I love what you do, great job.
P.P.S. if you think I sound creative or useful, I’d love to work for you in any capacity. So drop me a line at alex s @ blue hydra . com without the spaces if you are interested. I would jump at the chance to do some writing for the game or in the manual, either in game or back story. I’d be happy to send over my resume.