Well, the final of the Light trilogy games had Pyrope and Demantoid. The former is the upper crust and among the oldest of the Garnets, the latter was an Era 2 Garnet. Both were in a political alliance with Hessonite until she disappeared to contemplate what Steven had told her.
As soon as Era 3 began they went full-North Korea on their colonies, cutting off all communication and creating police states while invading incomplete Colonies that didn’t have Garnets assigned time them. They decided that the Diamond Authority was irrelevant, so a Garnet Authority would rule instead.
So unlike Eyeball, Aquamarine, and Holly who want the old ways back, the two of them want to create a new universe order.
Then we have Mean Lapis, who just wants power and looks down on other beings for wanting/being something else like an anime mid boss villain.
There’s the colonial Peridots who are content doing what they did before but for their own glory instead of their Garnet’s, and the colonial Bismuths who are still deciding what Era 3 means to them and claimed a colony for themselves.
Plus Emerald and Morganite were intended to be Era 3 villains. Presumably Emerald is a space pirate or something, so I guess a rebel without a cause. Morganite only really had two things that we know of, hating Fusions and wanting her property back, which would put her among Eyeball and Aquamarine but outranking them by a significant margin.
The only other thing we really have to go on for Era 3 identities for Gems is that Steven has introduced democracy and capitalism. We saw the former with the Zircon election although we do know they are also working together since there was that line about needing Steven’s help with something, and capitalism is evident in a Pearl being a tour guide and leading Gems to a gift shop.
Also, Hessonite is Batman now.