I've already had my two cents on the locations from that poll, but here I want to go into more detail about the subtle, and less subtle changes that could create some ideal differences for a potential Far Cry sequel, regardless of location.
ENEMIES: The Far Cry series tends to have the class system for its hostile (and friendly) soldiers. For example, both FC3 and 4 have "assaulters" armed with Ak-47s, "berserkers" with M133 shotguns, molotov cocktail throwers who are always blackout drunk, heavy soldiers with flamethrowers, idiots attacking with knives, and so on. This helps from a modeling perspective, only a few assets needed to create identifiable enemies that each have their own tactics and abilities (such as the charger's smoke grenade). Still, this system is very repetitive. An alternative, at least in some games, is randomly generated enemies. Sure, each class has some variation; one enemy might have a beard, another sunglasses, or maybe a small badge on his shoulder, but aside from that most NPC's will look and behave very similarly. Why not have some uniform differences (perhaps lootable)and weapon variation. The further you progress into Far Cry games, the more powerful weapons you acquire. Thus, the stock weapons of your enemies don't stand a chance. Instead of every assaulter being armed with an AK-47, maybe have some with Mp34's, P416s, and even new weapons. Have some wear armor to varying degrees, that affect their health, speed and ammo capacity. This could also put player exclusive weapons in the hands of NPCs. Maybe some enemies wield grenade launchers, and like molotov throwers, explode when you shoot their grenade belt. Or maybe some carry hand held SMGs' and rely on fast-paced in-and-out tactics. The possibilities are endless because nearly everything would be unique, resulting in a different play through each time. No two outposts would be the same, nor would the same enemies patrol the same outpost each time you play. This addition would really improve the dynamics the game, and make it feel much more alive. After all, with Far Cry's supposed survival theme, it would make sense that your opponents are also trying to survive in a harsh conflict.
(Also for some reason, Ubi likes to dress its evil soldiers in red, and friendly ones in blue. Did Pagan and Vaas each order a shipment of red pants? Must be pretty hard to come by thousands of red trousers in the Himalayas. Green Camo increases the difficulty of spotting enemies in thick foliage and is a bit more realistic, in my opinion. Especially for the irregular pirates and Royal Army.
VEHICLES: People ask for airplanes, or pilot-able helicopters, which would greatly improve the vertical aspect of the game. The buzzer was a welcome feature, but at times was a bit clunky. maybe vehicle takedowns could be possible from buzzer to helicopter. Flying vehicles create another play style that makes "every second a story." Vehicle takedowns in boats, which were strangely missing from FC4, might make boats a more interesting and viable way to travel.
ITEMS: Have actual models for the items, instead of essentially collecting a bit of humorous text. It could go as for as being able to pick up certain items from the world itself, such as the many beer bottles and food items lying around. They could respawn, but now looting chests would be more interesting. You could still have the trademark Far Cry witty comments about each item, but a visual to go along with it. Having more than one item in a chest or on a body would mean an improved inventory screen as well, instead of a "bag" with a bunch of text and values. These items could be quest related, say finding twenty packs of Kyrati royals. These chests would ideally be thematic, because who in their right mind would climb to the top of a crumbling bell tower to store a small amount of money and a maxi pad in a wooden container? (what is with Ubisoft and its love of climbing towers? Far Cry and Assassin's creed.
SIDE QUESTS: What happened to the side quests in Far Cry 4? They were just challenges or means to get high level gear through hunting. FC3 had them, and although they were a little stunted, they were pretty interesting. You could only do one thing at a time however. You had to abandon one quest to go on another, or do a challenge. Being able to have an agenda of things to do would make the world seem more connected in a future Far Cry game, because each activity would feel less separated from the main game. There should be more to do than just kill animals, or people and messing around with vehicles. Uncover backstories through quests, not by finding lost letters. If many side characters, even random villagers on the side of the road, had their own goals (NOT EVERY npc though, just some) it would make the copy-paste civilians more relatable and less like "victims". In a war, the two armies fighting should each have a common goal, but not necessarily the people. Instead of one person voicing a pitiful villager complaining about the Royal Army, have tons of variation in their behavior and attitude, at least at a surface level.
CRAFTING: Why does my level 3 ammo pouch have to be made out of tiger skin? It looks like it's made out of leather. Why can't I use sambar hide? Instead, there could be an entirely new system where upon killing an animal, the player could have a choice to harvest its pelt, collect bait, or collect its parts (I don't know, for selling?) Leather could be made from any animal, albeit fish or birds, and can be used to craft the same things, regardless of its origin. Obviously, some material would be better than another, but the right skin could increase durability or capacity for any given pouch or bandolier. How does Jason/Ajay carry all of his gear, he's got a lot of stuff. Pouches, quivers, fuel slings and more. These should encumber him, but they don't. I believe a loadout system could work here, say four slots for different types gear, so the player isn't always fully equipped to utterly destroy the enemy.
Each kill would mean something, and the player would have to plan accordingly, because ideally, animals would be rare, at least some of them. No more giant icons telling you were honey badgers spawn. Let the players work that out by themselves, so they notice newly added animal behavior. The rare signature animals, like the white tiger, shouldn't be easily located by giving the player a way point and specific area. Only a master hunter can find these animals, and make it out alive.
PHYSICS/NPC DETAIL; This is just a minor thing, but for some reason, in Far Cry 4, the enemies bounce around like crazy. I once dropped a dead guard off a three foot drop and he bounced thirty feet away from me and alerted the camp.There's something about the physics in the last two far cry games that feels off. It's often really clunky. New animations for take-downs and NPC movements (a lot recycled from FC3) might give a different feeling from the familiar sight of stabbing a guy in the neck only for him to fall clumsily down, always facing you, resulting in weird rotational issues. A new ragdoll system or more defined gore gives the weapons more of an impact than normal. Maybe if an enemy is wounded, his comrades try to carry him away. Maybe some enemies surrender or retreat, instead of the determined psychopaths in each game.
Alot of this may seem like ranting, but these were some of the areas that I have seen working in other series, and provide a unique experience. I admit these seem like a less crazy, more tactical Far Cry, but that's my preference. I actually like FC2's malaria feature, and its detailed world, but not it's constant barrage of enemies and somewhat dull NPCs. The version of Far Cry I describe here is still the bat sh*t insane playgrounds we have come to know from 3 and 4, but it's just a playground you have to work hard at to play in.