It’s just this generation’s New Thing. They’re making a big deal out of it because it’s a evolution of a feature in the third generation. Empire & Napoleon added controlled fleet battles, Shogun 2 added fleets interacting with land-battles in terms of bombardment, now we’re seeing contested army landings. To me that’s an indication of a TW: World War game in the long term.
Heck, thinking about it, there’s more. Artillery in Empire, Napoleon and Shogun 2 was developed to the point that cannonballs would deform terrain and had variable trajectory types for, say, normal cannons and mortars. Artillery would of course be a huge aspect of a World War TW game.
Firearms were of course added, and developed up to the point of gatling guns - not a great deal of work to do to get it up to WW1 standards. They’ve also added smoke shells, I seem to recall, which could dovetail into poison gas shells. Massive ironclads were added to Shogun 2, which also just requires a fairly short leap forward. Considering the massively important navy aspect of WW1 and WW2, this is a good indicator since it seems a lot of work was done on that aspect in Shogun 2 without quite being given the level of importance in the game that would merit that kind of work.
Rome 2 is supposedly adding customizable unit loadout on the cohort or century level. (One legion replacing the traditional unit stack “army”, ten cohorts to a legion, six centuries of between 60 to 100 men in a cohort - normally 80.) Which makes sense in a Rome game, but it makes even more sense in a WW game where you might need to change a unit into a zigouilleur on short notice*.*
Some details are still missing, of course. Like the submarine warfare mechanism and countermechanism, engineers to create player-controlled terrain deformation like barbed wire or trenches, flamethrowers, aircraft observation and to some degree aircraft combat, tanks, mines, tunneling and more that I’m certainly forgetting.