I agree with having wildmen, I think it’s low-hanging fruit the devs could implement easily.
A viking sub-faction of bandits would also be cool.
Classic round-shield chain-mailed small-arms brutes.
With both less worried about them bringing something unique to the table, I’d be into it just for the visual variety.
Perhaps for wildmen I’m thinking add wildmen as a massive force of individually ineffective skirmishers.
Weak reed/bone armour and headdresses, if anything, with some wood/stone/bone/bronze weapons would also be nice though.
Perhaps with a druid that can empower allies or sap enemies will, and a skin-shifter that can maybe turn an ally into a tank or control an enemy.