There's nothing new to add. If they tried a straight remake again, it would be mediocre, for all the cosmetic innovations they could do. The only choice is a variation, and since the studio in question has recently made a very good FPS, they could follow up with the same while their skills are hot.
I disagree heartily. X-COM is by no means some 'pinnacle of TBS elements'. It can have a lot more meat on its bones and I think it's a real problem that everyone who has tried to climb that mountain of success and has fallen off has failed to realize that the problem with their goal wasn't where they were trying to get but how.
X-COM was good; great, even. I spent very long summer holidays with it. I still have a copy installed. Fanatical? Maybe. But putting that aside: There's a lot of room for new ideas just for the original UFO Defense and TFTD.
Everything takes place on Planet Earth. Why? Why don't we ever take the fight to the aliens and do the first part of the game in reverse? (You build bases on the Alien's world, force them to submit, etc.) That's an angle we could pursue; maybe this could make the game even longer. So you
FINALLY stopped the invasion of Earth. What's their next move? Well, probably, they're going to wake shit up underneath the Sea. So you deal with that crap. By this point you're probably pretty tired of these aliens so why not bring the fight to them? Earth can take weeks or months to clear out and clear up and that's fine and awesome. But why do things have to always end with Earth? If the aliens are still out there aren't they just going to come back one day now that they know what kind of threat we are?
Why don't we have morphable terrain? Why don't we have targetable limbs? Why isn't research more modular/weapons more modular? Why can I only manufacture new things and not things like Grenades? For that matter, why are there only a few kinds of human weapons? Why can't those weapons be 'enhanced' by alien technology? Where are our procedurally generated levels? Why can't -we- spy on and infiltrate the aliens' bases? Why does all combat take place either on the ground or always in the sea with no crossover Why can't we stop a ship dead in the air and infiltrate it there late-game? Why can't we do mid-air forced boardings?
Why don't we have more civilians and more at stake? Why don't the aliens resort to larger measures over time such as sacrificing a ship to blow up a whole city? Why can't I guard meetings of Heads of State from alien attacks? Why don't aliens try to replace powerful figures like the Presidents of Countries? Why don't aliens try to use Biological Weaponry if we let them capture humans and cattle enough times? Why don't cities ever have any military support of their own? (National Guard, etc.)? Why can't the aliens capture and use those facilities against us? (AA Guns, etc.)
Why is Psionics so limited? All we get to do is drain Morale or take Control of an alien. Though very cool, why can't we just kill aliens with a lot of mind power as long as it drains Health and Morale? Why can't we 'suck' information from them then rather than waste time and money 'interrogating' them later? Why don't our interrogators use that Mind Control technique anyway? In fact, why can't my soldiers carry out interrogations of Aliens? In fact, we can intercept communications from the aliens; why can't we change the mission and location that a ship is going if we force an alien Commander to give them that order? For that matter, it's obvious we can triangulate where psionic signals are coming from -- why can't we make some sort of Detector other than the Motion Detector? Why
aren't there other sorts of Detectors other than the Motion Detector? Why can't I integrate those detectors into my soldiers' armors? Why can't the aliens be detectable on certain kinds of detectors?
WHY DON'T WE EVER GET NIGHT VISION GOGGLES or get huge flares to shoot up in the sky to make things bright as day in a large radius for a little while? Why can't we set up mobile floodlights and so forth? For that matter, why
don't we have things like flash bangs which only work on aliens which have eyes?
Why don't the aliens ever armor up? Why don't the aliens get detectors and all that? Why don't they get devices like EMPs which shut down electronic devices but keep theirs running? Why can't they put down traps for humans like our Proximity Grenades? Why don't the aliens ever try to capture one of the X-COM soldiers? Why don't they ever use that directly against you and use that soldier to find your base if they're not tough enough physically or mentally? Why can't you try to rescue that soldier if you have researched a sort of tracking device for your soldiers? Why can't you
set up that sort of encounter? Why can't the aliens get wise to it and just kill your soldiers on sight and mind rape any survivors until they get what they want and then kill them?
Why did the Interception phase get the axe in so many of the follow-up fan sequels -- why wasn't that improved? Why can't we make 'portfolios' of inventory (e.g. "sets of equipment" templates) to make outfitting our Squad better and easier? Why can't we give our troops ways to toughen up outside of combat (firing ranges, physical training centers, etc.)?
Why is base defense so static? Why don't I get to control my own doors and install turrets and so forth? Why don't the aliens get to try and disable those defenses while they invade? For that matter, why don't I have to worry about things like the security of my information network, my electrical grid, and my ventilation shafts? Why can't those have advantages in combat?
Why can't I get my soldiers to go to a "Standby" mode where instead of Reaction Firing, they spend their whole turn standing still, when something eventful happens they get their turn, and half of their usual Time Movement points?
Why can't my guys do things like suppressive fire to lower the Morale of enemies? Why don't they do the same to us?
Aliens eventually get weapons that fire around corners. Why can't we figure out a way to do the same? Why don't we ever seem to do things like Fire-bombs on the downed Alien ships (say, Napalm) to try and kill the Aliens that are out in the field at a cost of damage to the craft? Why aren't there more options in general when you're about to do a landing? Why can't I pick and choose WHERE I'm landing? Why don't the aliens get to shoot at me while I attempt to do so?
And on and on and on.
I can just list ideas from now until the day the cows come home. To say that it's "been done to death" is doing a disservice to ingenuity. Just because people aren't willing to try and expand on the original doesn't mean it's a bad idea to do so and doesn't mean XCOM has nothing left to offer.