I am just wondering, what kinds of things will never be doable in the game?
Many people like hex but that is probably one thing.
2D is likely another.
I don't know what might be added in and what won't.

I know their relunctance to tell us what will be added, since it may change later on, but can they tell us stuff that can't be put in at all, well without CIV5 in a decade at least.

Will all the stuff from previous Civs be reasonable?
I especially like the spaceship from 1 since it gave choice on launching sooner and slower or later and faster.

I know many things can be done with XML and Python and probably the SDK too but some not.

Spaceship should be doable - I too would like that. The after-launch space race was always the most fun one!

I don't think we'll be able to do anything major to the graphics engine, so, as you say 2D is out. Hexes seem to me to be something that would require building from the ground up, so I think I'll have to agree with you there as well. I also think that we won't be able to change the game from being turn-based... though why anybody would want to is beyond me.

2d probably will be possible. Just disabled camera rotating, and change all of the units/buildings/terrains to billboards. Insta 2d. And disable world view.

Depending on how much of the source code the SDK contains, potentially anything that does not depend on the graphics engine will be moddable. The statement about games "loosely based on Civilization" sounds promising. But since Gamebryo is essentially a separate product, we won't have access to its code, and will not be able to modify the graphics engine itself.
It wouldn't be impossible, however, to simulate a 2D environment by locking the camera location and replacing all models with detailed billboard images. Something like that could be helpful on older systems, to reduce processing needs.
edit: crosspost

2d probably will be possible. Just disabled camera rotating, and change all of the units/buildings/terrains to billboards. Insta 2d. And disable world view.I supose it depends on what you mean by 2D. The game would still render it as a 3D environment...

You'd also have to make everything billboard - terrain, buildings, resources... and it would still be rendered in 3D.

but if you want to make these major changes, why don't you just mod civ3 into a more civ4 game? it might be easier to do

Besides graphics and stats, very little in Civ3 is moddable. You can't change the way anything works. We could do far more with Civ4 from day 1 than you could ever hope to do with Civ3.

Real time battles a la R:TW

Teach Isabella to love me. Why, why do you spurn my advances Isabella!