Darkspear Raiders
The datamined faction description says these fighters are loyal to the troll nation and battle Theramore forces for control of their ancestral islands.
Theramore Expeditionary Force
The opposing datamined faction is described as loyal to Theramore and fighting the Darkspear Raiders over the islands.
What this may mean for PvP rewards
The presence of two opposing reputation entries strongly suggests the battleground may have reputation progression or reputation-linked rewards. The client data does not yet prove specific vendors, reward items, reputation rates or rank requirements, so those details remain open.
Separate from the Honor rank system
Developer interviews already describe an Honor progression path through Rank 14 during a season or patch cycle. The newly datamined reputations appear to be an additional Darkspear Islands layer rather than a replacement for Honor.