Battlefield 5's announcement trailer was not great—a vertical slice so convoluted you have to watch it frame-by-frame to figure out what specific features are being shown off, with a fake-looking HUD that makes it hard to tell what's 'real.' It didn't do much to communicate the most interesting ideas in BF5, which include an overhauled revive system and new squad features. That overhaul, not the setting or weapons or vehicles, is what's most exciting about Battlefield 5.
In Battlefield 1 and the prior Battlefields, only Medics could revive teammates, and they did so with the rapid plunge of a syringe. Everything about that statement is changing in Battlefield 5. There will still be a Medic class, and they will still be able to revive any teammate, but it will take much longer. A revive animation will play, during which the Medic can look around for threats and cancel if needed. Furthermore, all squadmates will be able to revive each other. If they're not Medics, they won't be able to revive teammates outside their squad, and their revive animations will last longer.
To further encourage squad solidarity, dying will not return you to the map screen. Instead, you'll spectate your living squad members and then respawn behind one of them. You're in it together until you all die, at which point you return to the map screen as a group with a spawn timer penalty. DICE also mentioned that we'll spawn with less ammo and gear than we used to, meaning it'll be important to have a Support player in the group for resupplies. Additionally, players will be placed into squads automatically at the start of every match to discourage lone wolfing.
Each individual change is fairly small. We could already spawn on our squadmates in Battlefield, so squad wipes were already important—does being able to revive a squadmate make that big of a difference? I suspect that, when combined with all the other changes, it could make a very big difference. It seems that Battlefield 5 is about squad play more than Battlefield 1 is, and that could change players' attitudes.
I don't know if this will turn out good for Battlefield. Maybe I actually enjoy the typical disarray of Battlefield 1 squads, which doesn't put too much pressure on me. But if the system works well, Battlefield 5 will theoretically be a better co-op game than previous Battlefields. I think my friends would be much more inclined to play a Battlefield game with me if we were all interacting more—physically passing out ammo (they are adding proper animations for everything you do), dragging each other's bodies to safety (this is a new feature, too), reviving each other, spectating each other. I'd love for my moment-to-moment experience with my Battlefield squad to feel more like Left 4 Dead, while the large-scale Battlefield tactics remain in play.
All of these features are confirmed, but I'm obviously speculating about what their effect will be. It could turn out that player attitudes don't change, and half of them jump into solo squads and lie down on hills. I'm sure some portion of players will only want to fly planes alone, and another will insist on breaking off from their squads at every chance. But even if the squad and revive changes aren't the transformation I think them to be, I'm glad that DICE has chosen to experiment with Battlefield's core systems rather than just put different weapons and vehicles into play—while also not straying too far from what Battlefield is and, say, pivoting to battle royale. (Update: Welp?)