Hiho!
The way combat in AI is done is quite a bit "old-fashioned". There is a lot of direct fire and only one indirect fire weapon (the grenade launcher). So basically nothing has changed in terms of infantry warfare since WWII. We know that this is not true.
I would love to see combat feel "more modern".
My ideas:
> more indirect fire weapons: Infantry Missile launcher with controllable rockets.
Can you still remember the "blaster bomb launcher" in Enemy Unknown? Something like that is available in the military today. It's not as powerful of course and you can't assign 219 waypoints, but it would be very nice if something like this existed again. Just allow the player to set 2-3 waypoints and a less powerful payload... this would leave some opportunities for upgrading (plasma technology => more damage, alien minicomputers => more waypoints).
The direct line of fire rocket launcher is almost out of date today. And the game is set in the future.
> something unique that doesn't feel like "infantry combat today": Force fields to create artificial cover
If there is some kind of force field technology in the game (I think I've read about it somewhere), it would be great to add something uniquely modern and futuristic. You could use the forcefield like a grenade, but instead of an explosion an area of power forms that can deflect/absorb damage and thus give cover to your soldiers.
Using smoke grenades is a very old tactic. Upgrading it to actually creating cover (not just obscuring visibility) would feel futuristic to me. One could further upgrade the efficiency of the force field, add chamelionic attributes (it assumes the colour of the surrounding environment and is thus invisible to aliens), etc...
> more futuristic ammo types: from "laser-incision" round (able to pirece thin armour by using a pulse of laser upon impact) to "anti-matter high penetration" round
Once the first alien armour appears ingame, one should be able to develop types of ammo for the "standard weapons" to counter it. I think it would add a flavour of futuristic battle if there was something like a bullet that is designed to use a small source of energy (e.g. laser technology first, later plasma, later antimatter,...) to "melt" through the armor on impact... alien technologies could open up even more improved types of ammo and thus keep the "old-school" weapons ingame.
I would love to use the assault rifle with an "anti-matter high penetration" round or a "plasma-core alien material jacket" round. If those were given cool names, this would add a lot of futuristic feeling to the gameplay (plus give you more things to research + keep the variety of used weapons higher).
I can't think of any more ways of adding more advanced equipment to the arsenal but perhaps there are more ways of making combat feel more like it was set in the future.
See you!
Andreas