1. More types of planets/gravity wells
Maybe more textures for them at the very least? Would procedural textures be possible...? iirc there are only maybe a half dozen textures per world type. They also come off as the same size, some massive worlds and some tiny worlds would mix things up a little bit, if only visually. Bonus points for tying it into gravity well radius.
6. Multiplayer support (better ranking system, in-game voting, anti-smurf etc.) and fixes (mini-dumps, lags)
The minidups and lag [especially late game] need to be shored up. I never played big online so I'm not sure how big of a problem smurfing is, though judging by some posts it must drive some people bonkers. As for the ranking system it won't matter much if you can't retain more than 50 active players.
7. Maps/Mods autodownload [including forge-made maps]
I always felt this hurt multiplayer numbers as much as anything else, there was no _good_ place to instantly exchange maps or modifications-- and since the MP count was never _huge_ to begin with, each time someone made their own map or mod it segmented online play further-- to the point where you almost have to have buddies who play in the same room or a group of close knit people who have decided on what mod/map pack to use.
8. Better and improved Forge and Map Designer
People love creating things, the more creative people can be with the Forge the more players you'll ultimately retain. I'd like to see Z-axis editing, militia editing, resource editing, gravity well size edit... etc. etc... Open it up as much as possible, you can still have the "quick map" options, but the people who seriously want to tinker should have the tool(s) to do so.
14. Terraforming, moons and other planets system improvements
I like this idea, though terraforming should probably be expensive and very time consuming. Moons would be a nice addition in my opinion if only to make it feel more like a solar system... the lack of moons kind of irked me... I'll leave it to the developers to best decide on how such a thing could be integrated into the game. It would also be nice if the planet surface reflected the upgrades of the planet in a more visual way. Ground based defenses would also be sweet... surface to orbit rockets and so forth, not tank battles or anything.
I know it's only supposed to be five, but the previous were really other peoples ideas and so to [possibly] bring something new to the table:
a. A larger variance in stellar objects that have properties that can propagate through all "orbiting" [or "child", if you will] objects. ie: People have mentioned stealth and cloaking as possible additions, maybe a specific type of star.. a magnetar or something could dampen early warning systems, or disrupt missile and gun tracking. Perhaps a black hole or other highly dense plasma matter star that "eats" errant ships that stray too close... or a white dwarf that cuts population drastically due to a lack of solar output. Bonus points for binary and trinary star systems, double mega jackpot bonus for binary and trinary systems with different types of stars. [ie: black hole munching on red giant]. Doesn't seem so likely given what are likely to be the "limitations of the system", but I can dream.
b. I know this is beating a dead horse, but I'd like to see more use of the z-axis so that it's not considered an "exploit" by a majority of regular players-- space is three dimensional [at least] and I'd like to see that fact exploited more. I don't think you're going to take away from the game by providing more tactical options for players to explore. I would also like to see the Forge include Z-Axis locations for stars and planets, so the galaxy seems a little less, I don't know, flat.
c. Better default effects for weapons employment and more variance in physical ship damage. This would cut down on the desire for mods and probably, ultimately lead to a more cohesive multiplayer community [especially if the auto-mod / auto-map ideas are a no-go]. I have a hard time playing vanilla sins ;_;.
d. Three words: "debris field harvesting". Seems a shame to leave all that glittering metal just floating there in space with no purpose except looking pretty after a fight.
e. More and better employment of tactical formations-- a little bit of echelon, some X, maybe wedge might be nice.
Ultimately the most important part is that it's ready for prime time on day one. It needs to be polished, as bug free as possible and smooth on midrange hardware. A lot of things can be overlooked or forgiven but buggy software, crashes, dumps and poor performance annoys everybody. An internal patcher [a la starcraft, and many others] can mitigate the patching and version difference problem. You should strive for as few version numbers as you can.
Sorry for going on-- I look forward to seeing Rebellion... whenever it comes out.
-Gonzo
PS: Collectors Edition.