Hawk, I believe you are correct in that 3D is not necessary at first. But then again, 3D is what sells these days, so like you say it may be a matter of a community effort.
Global Conflict Blue might have been such a good option, sadly the owner decided to close access to the source code.
On the other hand, such a complex campaign engine was planned for a community effort called Combat Simulator Project (
http://csp.sourceforge.net), however development has been slow and I'm not sure if at this moment, the scope of the project still includes such a complex item.
I believe a dynamic campaign is such a complex and non-profit oriented project, that it may take too long to develop and to stay commited, unless you work for a defense contractor in the distributed simulation business.
cheers