What kind of interface would hobbyists want? One that's easy!
Fortunately, anyone trying to connect an external process to Anteworld is likely to be a fairly technically capable individual, with C/C++ at their disposal, as well as maybe Java, Python and other scripting languages.
My vote, of course, is for the C/C++ based interface since it's the most commonly supported and what I've been using exclusively. Keep in mind that a good deal of the external interfaces - mainly for LED's and special controllers - all have their own SDK, and in my experience I've seen them mainly support C/C++ and Python. Those two give the best of both worlds: a lower level coding capability with lots of power, and access to predefined functions through a more straightforward scripting facility.
How to integrate this will be a design challenge. But, philosophically speaking, my strongest recommendation is to implement a strategy for external interfacing that mimicks, if not outright copies, similar interfaces for something like either X-Plane or FSX. X-Plane has a robust plugin SDK, FSX users have an application that *I think* accesses some form of shared memory, and reads/sets values by reference to offsets. In the main, though, just don't reinvent the wheel.
If you have used the entire JSBSim code base as a library in Anteworld, a straightforward networking interface is already built in, and I actually think you may have connectivity available already on a per aircraft basis via XML script. Take a look at page 58 of the JSBSim Reference Manual and see what you think.
By the way....what do you mean by "IG?"
