I'd say "Enemy Beyond" would be more suitable to an expansion pack than a sequel. A sequel should have an all-new subtitle pattern.
I can't see how the game could be expanded much further. The good news is that Firaxis has said that one of their big plans is to do right what Terror From The Deep did wrong: Lovecraftian X-COM. Hence, Enemy Beyond. Humanity has entered the big leagues post-invasion, and that's not the best place to be, fusion lances or not.
Not exactly sure what TftD added.
And, again, it seems to me that a sequel should have a different namescheme.
Another aspect is how EXALT is "going too far" with gene augs. This is a good idea, except the Elite EXALT augs aren't very different from what X-COM fields, so it comes off as silly. EXALT should have had a third tier, employing plasma weaponry and truly posthuman augmentation (genetics, mechanics, psionics, the whole shebang). The kind of thing you would look at and go "oh god what the fuck". The kind of thing you'd have to autopsy. And that would be when Vahlen should have given her opinion that X-COM should never go that far.
Something you wanted to say here, GWG?
Something I thought I had. Namely, that if TV Tropes is right, EXALT has augments far beyond what XCOM could hope for.
I still want my Stargate X-Com.
Playing as Stargate Command, going through the 'Gate to worlds to explore, get resources, and kick alien butt, defending against invasion, diplomacy with other worlds, research Goa'uld, Asgard, Replicator, Tollan, and others technology, perhaps a base invasion where an infiltrator shuts off the Iris.
Sounds like a good project for a mod.
Hey, maybe Enemy Beyond could include some mod-enhancing functions, like Civilization V or something?
Anyways...about this XCOM sequel. I've been thinking. According to TV Tropes, the aliens are invading to prepare humanity and themselves from some kind of external threat, right?
Well...imagine this.
Some decades or centuries past the Volunteer's sacrifice, the world is a different place, if much the same. Politics have changed a bit, but not as much as you might think. Technology, of course, has taken massive steps forward, especially with the development of elerium technology, advanced alloys, and the like, including Firestorm-like aircraft making travel faster and cheaper. War is different once more, as technology for MEC troopers, SHIVs, Titan Armor, and the like...but, again, much the same. Cities have been founded on the Moon, colonies have been founded on Mars, and there are mines in the asteroid belt. Psionics aren't common, but pretty much everyone not religiously opposed to them gets screened.
XCOM is still around, if gutted and relegated to more of a "sentinel" organization. It maintains a handful of elite soldiers, with titan armor as the standard. They discover an alien craft entering the system and crash-landing on Mars. They are sent to investigate, discovering a group of aliens. After fighting several sectoids, mutons, cryssalids, and other fodder, they get to the bridge, and defeat a couple elite mutons defending an ethereal, who promptly surrenders...and tells of a threat which is coming to Earth.
Hell if I know where to go from there.