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I think options for different outcomes can make things incredibly interesting. I love What-If's.
Science fiction has offered so many different types of scenarios that we could explore (Transhuman and otherwise):
Different types of Wormholes, time-space travel with iterative timelines (there are so many potential ways of this working), dimensional/multi-verse travel and interaction (also many different ways this could work), ancient progenitor civilizations, galactic archaeology, all sorts of bio-engineering future possibilities, both apocalyptic and idealistic, Alien jungles, zero-gee oceans and breathable areas in space (see Larry Niven's 1980's Integral Trees and Smoke Ring books for example), planet-free lifeforms, sentient parasites, accelerated evolution, alternate earths, living or moving cities or sentient planets, fascinating technological discoveries and implications (example, a technology ending gunfire; Arthur C. Clarke's The Trigger), engineering galactic macrostructures (Arthur C. Clarke's Rama series, John Varley's Titan, Wizard, Demon series, Dyson Spheres, Larry Niven's Ringworld/s) , undersea whole civilizations, exploring beyond universe bubble physics and macro structure, civs caught in time or slowed down in black holes (Vernor Vinge's Marooned in Realtime books, Fredrick Pohl's Heechee series), machine based ecosystems (James Hogan's Code of the Lifemaker and The Immortality Option), Living cities, life and civilizations living on stars (Robert L Forward's Dragon's Egg and Starquake), energy based life forms, and all sorts of interesting alien or just human civilization variations where different alien civs have all sorts of political, economic, and dominating relationships based on differing biology, technology, and philosophy. Also ideas easily and quickly pulled from wikipedia/google; Star Trek, Star Wars, Alien/s, many tv series, role-playing games, comics, and books, all realistic, interesting, and plausible. (note: I am well read and watched)
I previously mentioned the Kardashev Scale in the Galactic thread, especially the roleplaying variations like in Gurps and other sci-fi roleplaying games, I definitely agree they should be used for future era outlining. There are so many technologies/tech trees that can be ported with ease, (with good supporting explanations relationships, text, possible units, pictures, etc.) out there (internet) that could be used. I'm not saying the ideas are mine, just that many ideas have been mentioned in other C2C threads (as well as in other civ mods), and should be revisited since they have been mentioned.
The more varied and interesting the end game can become, the more fun the pursuit will be. Randomness, diversity, and variation is the spice of life.
I bet that with time a lot of these ideas can be explored in C2C.
You never know until you reach and try; time, experience, and imagination may be the only limits to seeing how far programming/modding C2C can go if you push it a little. At one time reaching the moon was thought impossible not to mention sailing across the ocean.
Imagine using multi-maps to load a separate save game for a time-travel or dimensional portal (no different implementation than loading a map for planets). Devise ripples of government policy or technology implications, displacing cultures, and having more macro control of civilization culture. Use bio-inspired fractally generated random behavior (like map scripts) to create weather map layers, plagues like yellow fever, or the bird flu, and other living world elements, like barbarians and animals, corporations and guilds, independent traders, missionaries, entrepreneurs, and other units that are sporadically and spontaneously generated in the word to give flavor. From Vanilla civ to religion, to corporations/businesses, to great leaders/villains, to weather, multi-maps, changing terrain features, diseases, ideas for controlling major trends and memes which could have some major civ changing impact. Literally the sky's not the limit. The galaxy is. (or more). (ps It would be nice to know what people think of these ideas.)
I know some of these ideas may be ambitious, but some are no different than having the right technology, or unit, or set of tweaked scripting, some things may just take time.
The future is everyone's for the making. The future era's in this mod as well as the future for this mod.