Stop using the in-game systems to separate the playerbase.
1.) Let us queue up for any piece of group content. Regardless of difficulty and chance of failure.
2.) Allow groups, guilds, and communities to be cross-faction. And cross-server for that matter.
3.) Use currencies better to supplement the loot lottery. There should always be some sort of progression ticking away when you do content in an MMO.
That's what i would suggest to start with.