I believe anyone would find the source code extraordinarily difficult to modify for our ends. All my experience (anyone else?

) with the game suggests that the AI engine is constructed to cover extremely limited sets of circumstances.
A couple of examples (my apologies to anyone who has never been a serious programmer):
1. The AI is only able to build units from a very limited source pool. Thankfully someone thought to make Improvements able to spawn units -- but consider that this might have been a programming workaround; if so, consider how extreme that is. So the source code for how the AI chooses to build units is not only extremely limiting, but probably a terrible foundation to try to meaningfully expand. So you wind up gutting the code there and redesigning it from the ground up. What algorithm would you devise to handle the 750 or so different types of units Wyrmshadow's built for SOE?
2. Consider Governments: Communism aside, governments in the vanilla game become available in an order which marches in lockstep with decreased corruption. One can only hope that programming Communism wasn't too taxing for them. So scrap another chunk of the "AI".
My guess is that this reflects a design approach prevalent throughout the code; those are just the first examples that came to mind.
To put some perspective on upgrades -- anybody want to even try to devise the algorithms to make the AI use artillery in anything approaching an intelligent fashion? (I.e., draw out the list of rules the AI should follow concerning all aspects of artillery.)
-- And nearly everything on our wish list, from Civ1-style revolutions to adding event triggers, almost certainly requires as much, or more, work as these.
In short, I can't see a way that a set of major functionality upgrades (and nearly
every feature would be) could
ever be financially worth anyone's investment. Which means it also wouldn't be worth it for
anyone to buy the source code, unless it was some lone and wealthy Civ fanatic willing to underwrite the project.
So all this is why I'd be really, really happy with an editor that worked closer to spec than the current one does, as well as expose the Teleport buttons etc. And even that assumes that the APIs the current editor uses are adequate, or else there goes the budget again.
Not Without Apologies,
Oz