Hypothesis: The Workgroup Missions
Well, this is a my very, very, very, etc. personal opinion and It refers to Soldiers Inc running on Plarium.com side. (so, it is not necessarily be of interest to other running implementations of this war real simulator):
I have observe the fact that this war game is designed, since its conception, to be the theater of war of immense military engagements, and not to small skirmishes.
The problem is that the human microcosm that populates the Zandia seems reluctant toward epic battles.
Perhaps, the limit of 150 associates for single combine may be a sort of bottleneck. Furthermore, even if this involves an enormous engineering work, could be very useful new "storyline", like project torchlight / syndicate contracts...but on workgroup-basis.
Make a stupid example:
For access to new missions, need 10 associated members. When 10 members have formed a assault or defence group, [under a "team leader" or without, the mission start. Any new level of mission, need new troops from the 10 members to start and go at up level. A sort of "workgroup", to increase interest in the game.
This hypotesis work also very well for the six partnership in join ops center. Six players in partnership work together to completate new contracts (ideal for creating cross-cutting interests among players of different combines).
If it comes up with a farfetched, do not be surprised: it's too hot in this accursed desert and the air conditioners are surplus of the colonial era! AHAHAH (for spanish: JAJAJA)