Amigo, I'm delighted by all that's going on! C3X Release 7 is truly amazing, but my original notion in kicking off this effort was indeed to build a full, "new-from-scratch effort" game, adding in bits like genuine AI-like behavior by the AI (I've written numerous posts on this.) I / "we" understood from the outset that there could be any number of possibly unrealistic paths to that end.
I remain of the opinion that a much smaller effort (meaning, smaller than the hundreds of thousands of lines of C code written for FreeCiv) could be devised, still using blocks of C code (or whatever language turned out to be the best "fit") with a relatively small number of OO templates.
As for the code in question - Yes, the Firaxis source code. I've reached out to Soren Johnson on the matter, and he did say that he would be contacting Firaxis about this, but he does seem to be quite busily, happily, and fruitfully involved with Old World.