I believe that expantion should not just bring new content, but also should evolve the content already existed in the game.
So while fantazising about how expantion gooing to be in AoC, i had this idea that Nodes should evolve beyong the Metropolos stage, for exemple a world hub that exist only if there's five metropolis within a server and only one node can achieve it.
Once achieved, the server unlock a new class "The engineer". And yes, i took a lot of inspiration comming with some of the names from guild wars2, since it was my main mmo.
here's my own take on the different combinations, i had a lot of fun thinking about these names and the meaning for what each class represent.