Oh you should see the 2.5 MedKits. 2.4 makes Fallout Medkits look weak... 2.5 makes them look overpowered. Any solid hit inflicts a status wound and bleeding damage and Medkits only heal a couple points. It's a very harsh but a lot of fun. Do note however that Medkits can heal grazes and other minor damage even if you're not bleeding. You can heal people once after they receieve damage or until they stop bleeding, whichever takes longer. So at best you can counter minor grazes and make up for a little more than bleeding damage.
I don't think I know any game of this sort that's dared to come so close to realistic in terms of combat and damage. It's often not a question of getting them back in this fight but ensuring they see the next one.
I don't think certain concepts require "adult" only labels. You're better off showing kids what things are like by dealing with them then trying to pretend it doesn't exist. I think the games that let you do evil things and kill children and such are actually better at teaching morals because you can try out the concept in a safe environmental and realize how lame it would be. Nothing like killing an entire town, realizing they don't respawn and you no longer have anywhere to sell items. Of course there need to be reasonable in game consequences, over the top games like Grand Theft Auto don't really work like this.
Still, I'm not sure the Drugs would fit the setting as nicely as they did Fallout. Phalanx seems to be genuinely concerned with the welfare of its soldiers and injecting them with massive doses of chemicals during battle isn't good in the long term.
On the other hand there's one I missed from FT that does fit. Dogs. Dogs seem to come and go from warfare. In ancient times they were big, Napoleonic warfare (which gets my vote for most absurd) ruled them out, then we saw them a bit in the World Wars and out again for the Cold War and Vietnam, but now you seem them in use again more and more. The alien war would still have a use for them if the Stealth system was in and it wasn't about pure LOS. Dogs would be fast and excellent scouts but harder to armor and only useful in combat as a last resort.
They probably need a good stealth system and hidden bombs and stuff to be truly awesome but maybe when that day comes. And if dogs don't seem up to the rigors of the aliens war, well it's 2084 and they may well be from a genetically enhanced breed.
I like you're vehicle idea. A bit like what they did outside battle in FT. Of course for IN battle there are going to be some kind of support craft, UGVs, based on concepts from X-com. I don't know much about this system really but I could see it making BattleScape vehicles a possibility. I also wouldn't worry about space, aircraft are among the largest war vehicles so a space that can fit the dropship could fit most ground vehicles as well.
As for the rest. I doubt know if Bethesda (they just beat Interplay in a lawsuit over this only to apparently sit on the franchise rights) would be down, but you can't copyright a game mechanic. This means we can do the same things but we can't have "Deathclaws", sort of like how UFO has Taman and not Sectoids. I was thinking a hybrid setting in which the Earth had technically won an alien war but with the loss of most cities and alien lifeforms forming their own ecologies in parts of the planet.
One thing I learned about Fallout Tactics is that apparently it was rushed to publication once the first playable version was done but before all the final polish got in. The backlash it got was because people wanted Fallout 3 and most in retrospect agreed it's good for what it is. I put it a bit behind 1 and 2 not because of genre but because it never got the finishing touches it was meant to. It's a good game even so, I just wish it had gotten more attention and the sequel that was supposed to use dialog.