Make a Current-Day Start game that has a 500-year timeline, similar to EU-series game play that lasts hundreds of years. Use near-exact current day tech, military platforms/weapons, national borders, space platforms (to include some space trash), ongoing national disputes (Taiwan, North Korea, Crimea/Ukraine, etc.).
This way, there's not a debate about "how it turned out" historically - the history to current day is a "known product" -- but the future is to be made, by the gamer.
Blend a CK2 and EU approach to the game. Allow some mild fantasy to a point (perhaps with an On/Off selector for Fantasy flavor). Not that we would need a Chess game with Death while exploring on Mars...
Improve the factored tactical combat compared to the elementary combat play of EU series (along with improved Retreat in tactical play).
Title? Hmm....howabout, "Alternate World Future (AWF)" or... "Future World" or... "Johan's Dream" - or since it could last 500 years, call it "Half Millenium"
Other thoughts/concepts:
Limited Terraforming potential over time?
Underground development/cities, especially in places like Antarctica and Greenland (lots of Geothermal underground living potential, if you have never heard of that before).
External planet exploration but keep the science at the pace we are now, slow creep and technically difficult to do anything of significance in space (as it is now), and lethal without the required resources and planning, such as - must go underground on Mars, because surface development will never be feasible (that's just Hollywood to show surface systems of colonizing Mars).
Lunar exploration/colony potential, but minimized to more realistic numbers and resource intensive requirements.
Armageddon potential (first DLC? ha...).
No Aliens, keep it real. We have Stellaris if we want to imagine all sorts of Aliens.
Potential that some parts of Earth could get anti-tech events due to EMP events, potential for DLC that returns Earth toward a medieval period (not to rehash EU series, but could use the game engine and setting of a future dystopian world where a mix of future tech and old-world street smarts could butt heads).
You have Half a Millennium of the World's Future ahead of you - "have it your way" or "I did it my way" (complete with a robot upgraded to mimic Sinatra).