Ok, so if I understand the latest rumors correctly, at 2000 points you can take a 2nd FOC, and allies may actually be in addition to this. So... let's see what broken combos we can come up with. I'll start us off.
1) Sanguinary Guard + Tau Crisis Suits
This one I'm really looking forward to. Everyone's jumpy, the Tau have awesome firepower, and if you put enough shield drones on the Crisis Suits, they get VERY annoying to deal with. By the time you do, the SangGuard are in your face. :)
2) 12-18 Obliterators + Fateweaver + Chaos Bastion
Ugh! This one gives me heartburn. What's more annoying than playing against Fateweaver? Well, how about 3+ cover with re-rolls for one of the nastiest shooting units in the game? Add in some Bloodcrushers and... ugh!
3) Orks with 90 Lootas In A Bastion or Aegis Defense Line
Gonna happen. Gonna suck too. Especially if they can take a Farseer too. :/
4) Eldar Runes of Warding For Everyone.
This is actually a good thing, since
5) Blood Angels + IG
Decent of Angels + Astropath = 2+ reserve rolls for the 2/3rds of your jumpers that you put in a single reserve group. Fun!
6) IG + Grey Knights
Though henchmen were annoying? Now they get actual melta-vets.
What else can we come up with?