Blood for the blood gods and skulls for the skull throne- War and glory!
This game's combat is pretty neat, aside from the occasional weird city siege (the enemy immediatly retaking it, or sea-sieges going weirdly), but I know of ways to improve it even further.

The spicy addition of more units! Who doesn't want more unit variety?
Especially in the industrial era, when all fancy new techs started rolling out.
Firstly I believe that the industrial era European civs should receive a tiny itty bit more unique art in their unit artworks to reflect the Napoleonic uniforms (The French wore blue, or the infamous red pants, lol) Not to mention, those black Prussian uniforms, or those Russian dark green uniforms. This is doubly more important with the riflemen unit, which depicts them as a WWII soldier. For example, the French depiction lacks the Adrian design, and the Adrian helmet was even shown during their "Lucy" trailer way back on December 10th, 2020! Oh dear! (Timestamp 1:03)

Secondly, and not everyone may agree with me on this, would be the addition of those wacky WWI vehicles. You know the ones: The landship tanks, armored cars (closest we have is the AA vehicles right now), or the big scary zeppelin (an early bomber, but very vulnerable to air attacks!). Perhaps even an in-between unit between the ironclad and battleship: the dreadnought. (Please see "HMS Dreadnought" on Wikipedia for further aesthetic details) I personally think they'd add a bit of flair, and utilize the coal/oil resources for an empire as fun new toys (or terrifying monsters to an unlucky musketeer, conscript or line infantry). However, this might reorder how the Tracked Vehicles technology is positioned on the tech tree. Could split it into two techs, with a Tracked Vehicles tech, and a tech named Tank Warfare for WWII tank technology.

Thirdly, the tweaking of unit weaponry and cosmetics. In industrialized warfare, the unlucky soldier may face an enemy with rifles and machineguns- but also flamethrowers, grenades, and submachine-guns (less range, more damage?) I overheard that Endless Legend had the ability to switch up weaponry and armor. Could this too be incorporated into HUMANKIND?
Fourthly, and probably the least likely: Future technologies. Attack drones, lasers, railguns, space weapons, or the classic gigantic death robot (REAL SUBTLE, yeah right.) There is minor potential.

FalafelFanatic wrote:

I'd like to see a Civilization route. Split Contemporary era into a Modern era and and an Information era. At the very least the Rifles feel very out of place by the time you're running around with modern armor. If we split into an Information era in an expansion with new cultures- new cultures means new art! Maybe we could get thematic vehicles that would make end game armies feel different.

Indeed, yeah. Even with our current ingame cultures, their uniques/bonuses helped to tell which time period they can be. The way I see it, here's the split looks like.

Modern Era

Brazilians - Agrarian

Egyptian - Aesthete

Soviets - Expansionist
Swedes - Scientist

Turks - Agrarian

Information Era

Americans - Expansionist

Australians - Builder

Chinese - Merchant

Indian - Aesthete

Japanese - Scientist (swap out the Reisen)

Nigerians - Agrarian

Just adding more units for the sake of diversity is not enough, there also need to be a reasonably abount of time the unit is relevant otherwise what is the point? Therefore beside new units, you also need to introduce additional mechanics (like attack bonuses and weaknesses) and technologies which introduce the new units and make it fit better with existing mechanics like strategic resources and polution.