|It's clear you guys have no idea what you're talking about when it comes to multiplayer and it's clear you don't have the talent to make it happen creatively or technically.|
That is a very strong statement. It is also, structurally, falacious.
The design (and production) choice to not implement multiplayer has no bearing on whether or not they could
do it. Just like not picking up a piece of trash doesn't mean that you couldn't; it just means that you can't be bothered at the moment.
As for the relevant question of what other features would one want for an expansion:
* Espionage. Do something more with it. Possibly even an espionage victory, with espionage techs.
* Planet Defense and specialized military units: Say, planets can have planetary defense grids capable of killing off whole fleets. But, bring along a special planetary siege ship, and that grid drops. Planets can have shields, which requires a huge fleet to breach, but bring along a shield-cracker, and it goes away. These should be in separate tech trees. Starbases should be able to build similar modules to protect themselves. The goal is to slow down invasions and allow someone to be relatively strong without having to have a large military. The downside is that it takes tiles.
* Influence Defense Starbase Modules: There need to be modules that can protect a planet from influence attacks.
* StarBase Galactic Wonders: A new kind of starbase. Requires building a new base of a new type. If you research down a particular tree long enough, you get a series of modules to build. If you build all of those modules on a WonderBase, it provides a massive (galactic wonder-quality) effect. The benifits are that they don't take tiles. The downside is that they're starbases, so they're vulnerable.. And there should be lots of useless modules to build between the initial base and the actual wonder power (or perhaps a gradual increase in ability). The Wonder Base, if destroyed, can be rebuilt by another side. Eyes of the Universe should definately be one of these; that way, it wouldn't be so incredibly powerful.
* Starbase capture: Resource bases, in particular, should be able to be captured. However, this requires a new tech and a new ship module.
* Starbase Interdictor Ships: A ship module (big) that suppresses the output of non-resource starbases inside a particular radius of effect. It must be stationary for a full turn before it becomes active, and it can't move while active. Using one should be considered an aggressive act, of course.
* Better battle visualization: Play Wild Arms: Alter Code F. It's battle visualization is very dramatic and very effective. Learn from it. It does have discontinuities, but nobody cares; it looks really cool.
* Planetary Siege Missiles: A module built onto a ship that allows it to function as an orbital bombardment missile. When it "invades" a planet, you can select a non-wonder improvement to be destroyed. If you have no espionage, then the missile picks something at random. Should be a very expensive, very large module. It's better than orbital bombardment, because it's something you could see coming (if you're not close to the source), and the missile is expended, so it can't be done forever. Also, siege missiles would be stopped by planetary defenses, as above.
* The "Genesis" Torpedo: A ship module that turns a ship into a "Genesis" weapon. It can turn a Class 0 world into a higher-quality one, depending on your society's "Genesis" rating. The ship, of course, is lost in this act. You should only ever be able to use like 3-5 of them (neutrals get one more) in the entire game, but there should be a new branch or two of the tech tree to support them. They cannot be used on already inhabitted planets. Improving your Genesis rating would improve the quality of all previously Genesis'd planets.
* The Anti-Genesis Torpedo: A ship module that allows you to unGenesis a previously-Genesis'd world. Not unsurprisingly, this is considered a hostile act. Previously Genesis'd worlds need to be indicated as such, with perhaps a fragile ecosystem or something.
* More explicit control over galaxy generation: Perhaps via some kind of Lua scripting interface, were we can specifically determine where stars go, how many planets they have, and which stars are homeworld stars. Failing that, just better control over galaxy size and number of planets and habitable ones. Real numbers, not "phrases" like "abundent". Actual percentages. And being able to select galaxy sizes based on actual numbers of tiles (5x5 is too small, but 8x8 is too large for my tastes. I want to increment by 1).
* Bomb Them Into the Stone Age: An invasion tactic: Your goal is to raze the planet to the ground, killing everyone who isn't on your side. The enemy should get a population bonus, because the non-tax payers are going to come out once they realize that you're trying to kill eveyrone. The result is an uncolonized planet. Perhaps an added version could include a mass-driver one, but it would drop the PQ. The purpose of this idea is to get rid of buildings that you don't want and can't ordinarily remove.