A month or two ago, I posted that people should give double force organizations a try. I don't really have an agenda (ie, a secret I-win-list just waiting for some sucker to allow me to use it, really I don't)
I just think the points will balance out most lists anyway, and I think some armies will find better balance - I have had lists where I maxed out heavy, fast, and troops, and had to take elite simply because I had points left over.
Anyway, most tournament people apparently didn't agree with me, and GW apparently noticed that people were not buying into the double force org idea, so they made the new Space Marine Codex.
According to this codex, you can take one chapter, and then take a different chapter as allies. Granted, this is not exactly double force org, but it does give you an extra HQ, 2 Troop, Heavy, Fast, and Elite - given a 2000 to 2500 game, you will probably run out of points before running out of slots.
I wonder if tournament organizers will start letting other armies ally to themselves, as a limited double force org (and I admit the idea of facing 4 Heldrakes is daunting enough, forget about 6... although at that point, are 2 more Heldrakes really going to make a difference?)