I really like the idea of taking sides with either the Villagers or Illagers. Here's an idea I had for having a way of taking sides.
The Illager trainee is a block and a half tall and wields a wooden sword. This mob will spawn near 1 village and 1 outpost. When the player gets within a certain range of the mob, it will run up and follow the player where ever they go. Now the player has a few choices. The player can either, kill, take it to the outpost or take it to the village.
Killing it will lose rep for both Villagers and Illagers.
If you take the trainee to the outpost the Illagers will not attack the player. The trainee will grow up to be either a Pillager or Vindicator. Raids would change slightly, making the bar go down when killing Villagers. You cannot trade with Villagers and they will run from the player but you can trade with Illagers. Naturally Spawned Iron Golems will attack the player if sided with the Illagers. You are able to get the armor Pillagers wear by trading with them.
If you take it to the Village however, it will grow into a new mob called the "Reformed Illager" and this mob would help defend the village but you cannot trade with it.