Thanks for the response. Someone correct me if my understanding is wrong on any of this- I'd like to understand more about this since it seems I like to push the limits here.
Barb World only uses the Barb AI. Barb Civ allows Barb cities when they reach a predetermined size to become a Minor Civ. Then the Minor becomes a Full Civ thru is prerequisites.
Barb Civ and Revolutions can push a game to have a total of 50 Civs (player included). But REV and Barb Civ is Not supposed to let any more than that.
But I've just thought having Barb World on would cause more barbarian civs to pop up than would otherwise spawn because of the earlier cities being more likely to qualify to emerge. That's a tradeoff I guess I ought to consider if I don't want to hit the civ cap in games. I just think that it's a shame when proper rebellions don't occur after the middle game because there are no slots left for a new civ to spawn. It's a good balancing mechanism to bring down the larger civs.
Rewrite the game engine and the DLL to match.
The game only supports 48AI (Civs), Player, and the Barb AI = 50.
So it's more than just the DLL- it's the game engine too? Where is that housed, inside the game executable? (If so then it's a black box, isn't it?) How then has the civ cap been changed in the past? I thought that just the DLL had to be recompiled, or something.
And anyone playing with 50 Civs on a Giant or Gigantic Map is asking for CTDs Mid to late game. And/or MAFs.
I won't deny you there.

I can't say I haven't been warned before either.
(I've never seen "MAF" before; "memory allocation failure" seems like a reasonable meaning considering the context though, so I'll assume it stands for that.) What takes up most of the system memory though? I would have thought most of it would be units and cities, and having more civs doesn't really increase these, it only changes the ownership. The real culprit there would be the bigger map sizes.
A lot of civs also end up dying eventually anyway, unless the game is very peaceful for some reason. Do dead civs affect stability?
As far as CTDs what kinds of things cause them? Bad AI logic? If so, more AI's would definitely increase the chances of a crash. I really like the larger amount of civs and larger world though.

It's more realistic. I'm even willing to work around increased odds of CTDs by reverting to previous saves.