New Idea for Faction Attainment
Instead of the same old grind of kill x number of mobs over x amount of time to gain x amount of reputation, why not introduce a long quest line that involves performing various deeds and rituals for each faction to gain the trust needed to deal with them. These could become increasingly more complex and difficult the higher you wish to climb on the faction ladder. Don't limit it to Kill the centaur of googlymah and then kill the goblins of makdar. Make it involving and have depth and meaning.
How does that sound?