I was talking to KarateKid about double force org recently, because I heard that the Golden Throne tournament was going to allow it - the first tournament of its size to do so. What struck me as funny is that when 6th edition came out, a lot of people didn't like allies, but allies were allowed - because it was part of the rules. Double-Force org is also explicitly allowed in the rules, like allies, but it was almost universally rejected.
There was a lot of debate about whether Forgeworld was REALLY official, and it was still more accepted than double-force org.
I understand that there are some silly combinations that are possible with double force org, but there are some pretty silly combinations available with allies and Forgeworld as well.
In the Golden Throne Tournament, according to this BOLS article, only one of the top 8 had a double force org (and each of them played against multiple double force armies to get there).
Although I cannot speak from experience, because no one plays double force org around here, I suspect, since the books are written with the understanding that allies and double-force org are part of the game, that GW balances the new books around those rules (I know there are cynics who would argue that I am giving GW too much credit, but who knows).
Anyway, this is my argument to give double force org a try, or at least try to build a list, and see if you can make it as unbalanced as you think (better to play it) - I am betting that the extra HQ and two troops eat enough points that even if you make a killer combo, there will be some weakness that can be exploited by an opponent (assuming an all comer's list).
It has always been true that some armies only had one competitive list. Allies helped us get away from that a little, but some armies are fairly limited in allies that they can take and, even for the others, there are only so many army combinations (because there are only so many armies to combine with). I think that double force org is the next step in creating an environment without net-lists, because it makes more possible combinations than allies alone.