I get the impression that about half the people responding to this
thread don't want Civilization to move into the future.
That's ok; but I would like to see it, myself.
This is the form I would like to see it take:
I think that Firaxis should create an interface making it possible to combine civ3 maps. This interface could take the form of a solar system map.
How it would work is this. You pick a scenario map or go to the Civ3 editor and create one. Next, you go to the solar system interface editor and link your chosen scenario to the solar system map. More than one scenario map could be linked to the solar system map.
The linked scenario map would appear in the solar system map as a planet. A space ships could then travel across the solar system map to one of several planets. On arrival in orbit, the player would be presented with a land option button. The land button would swtich to the Civ3 scenario map and allow the player to choose a landing site. After that, the game would play as it does now on planet.
If the player decided to return to space; the space ships should have a launch control(button) available. Furthermore, the solar system map should be a playable scenario in it's own right. Space ships should be able to engage in combat, blockades, stealth missions, troop transport, space piracy, etc.
Ultimately; there should be something like a worm hole or jump point in the outer reaches of the solar system that would allow transition to other solar system maps.
Since this solar system interface would use Vanilla Civ3 and Civ4 PTW scenarios; it would be completely customizable. Anything that works with these versions would work with the interface. Customizers would have a whole galaxy of new possibilities: space ships, alien creatures, alien races, alien artifacts.
This could make Civ4 truely great not just more units and Civs.
For those of you who don't want to move into the future; just don't build space ships.