So as I was reading through the website I realized that neither faction is actually evil, they are both good and bad based on perspective, but I thought it might be interesting to actually be able to side with a third, truly evil, faction that is aligned against the other two. I suppose it would be a faction lead by Regulos and you would be working against the other two to destroy the world.
The third faction could be a whole complete faction with their own zones and land or they could be added in a way similar to how LOTRO does Monster Play, where they are only played PVP in certain areas and maybe in the case of Rift, you could participate in the "spontaneous events" mentioned on the website. The LOTRO Monster Play method could be done two ways, like LOTRO you could start out high and just fight the higher level characters in instances or you could alter the concept and start out a level 1 and get xps for participating in the events and level up an evil character or monster so you can participate in higher and higher level events. I'm not sure which works better or at all, but it would be interesting nonetheless.
If the third faction was an actually fully fledged faction with their own areas, towns and strongholds it might be pretty cool to run quests terrorizing the countryside, fouling the land and doing reverse instances where you are pushing the heroes out of the dungeons to reclaim them.
Anyway, I just though I would post on it and see what ideas people had. I realize stuff like this can't just be tacked on, but I thought it would be fun to think about what could be done in a future expansion.