This is not my idea, but something I saw in another thread that I thought could use highlighting.
When I said 'Tribal Forest Dwellers' what I was thinking of was 'Wood Elves' but knowing that Elves don't exist in Elemental's World, I offered a counterfeit substitution but with the same image in my head.
Bows, leaves, leather armor, green cloaks. Yay cliches.
Still, would be noticably different then how most of the factions operate in beta. At the moment Stealth and Ranged combat aren't really very effective tactics for long-terms, and you can't build inside of forests.
SOURCE: https://forums.elementalgame.com/386597/get;2674219
This doesn't have to be wood elves, but some environmentalist or druidic faction.
The ability to build on various tiles could distinguish other factions as well.
An image comes to mind of "cliff-dwellers"--but building on impassible tiles could be too big an advantage. Cliff-hugging structures may be a technical challenge, too; though you do have rocks and things hugging mountains now.
Building on water could work. That could be unlocked by technology, too. Or only for certain building types.
I like the idea of factions living in or adapting to different environments.