The deuteragonist would've been MARSOC Captain John Myers. He would've been struck by PTSD, a major plot point for the overall story.
Typhoon wasn't implemented until after the confirmation of the missions. The name and concept of Typhoon was taken while designing Just Cause, the second mission in development after Walking through Caracas.
The original enemy faction was an Iranian terrorist group, lead by a CIA agent gone rogue. They would've blackmailed the United States government to give access to Iron Wolf documents and later would've taken control of it.
The 2033-storyline was actually written as a post-game view on the aftermath of the Iron Wolf strike. The characters were also different from the Predators, but not designed in any way.
The original mission list contained "list-missions" and they were playable through the eyes of Spike. The missions could be selected in different orders and would've had different outcomes depending on what intel you gathered in other missions.
This system is somewhat like the cancelled worldmap feature in Warzone, only on smaller scale.
In later stages, the 2033 missions were designed and would focus on a civilian resistant force more similar to the Predators. They were less militarized however.
The mission name Walking through Caracas was originally a placeholder, as all mission names would've been placeholders in the structure of "verb-preposition-noun". The name Walking through Caracas stuck however.
The enemy faction for the 2033 was originally the state of California, which called out to be a country. The playable force would've been in the state for unknown reasons.
The locations for the 2033 missions were scheduled to all be in the Americas, being in order from northern to southern locations. The concept was that the resistant force would've been able to travel on foot, due the lack of available vehicles. This was dropped when AFO Predator was designed.
In very early development, 2033 was in the year 2050 in a more dystopian America. The playable faction was a similar resistant group, who needed to be unrecognized at all times.
The reason the weapons in Walking through Caracas were deemed as placeholders, was because the developers were still pending which weapons to include. They doubted between very old russian equipment and more modern equipment. The latter being chosen at the end.
The multiplayer was originally going to be replaced by the new Battlezone, while Battlezone would've been more similar to the Warzone-style.
The opposing factions in multiplayer were originally player customized clans, rather than the generic Predators vs Typhoon. The multiplayer clans would've been customized to the degree of which side it was on and would've been matched to it's opposites.
Gear would've been much more important and had greater effects on performance of the character, besides small additions.
Various gamemodes were cancelled. One gamemode, called DefCon, is available on PC using hacks.
Attachments were inteded to have no restrictions. Balancing issues made it not appear in the final product.