Variants are fine, indeed part of what makes near future SF fun, but it seems to me that 2300 is built on the assumption that something happens in the late 20th/early 21st Century to derail the current forward march of technology. Dropping it entirely would alter the "present" of 2300 significantly: not a problem for personal campaigns but it would make newly published material incompatible with the previous edition.
Ever consider the idea of dual timelines existing side-by-side? I this setting the Twilight war both happened and did not happen. Something happened in 1990 Russia during the coup. In one version Boris Yeltsin was killed and the coup plotters succeeded. The Soviet Union was still in decline afterwards but went out with a bang rather than a whimper taking the United States with it. The Twilight War happened as did the the original 2300 timeline. The other timeline is our timeline up to 2003, this timeline gets vague between 2003 and 2050, but by 2050, the US and several other nations have colonies on Mars. By 2100 a unified Martian government forms. Perhaps the war of terror continues as well. By the time 2300 rolls around the world looks different from the old 2300. In both timelines the stutterwarp engine is developed. the barrier between these two universes is somewhat thin. Perhaps certain events can lead to a transfer from one timeline to another. The Stutterwarp for example when not working properly might cause a transference from one universe to the other. Certain ancient artifacts discovered on unexplored planets might cause this transference. Perhaps time travel from the future was involved in changing the timeline. A visitor from the Future might have either caused World War III or prevented it. Perhaps a third campaign could evolve between competing Time Travellers from different time lines. One could be French and the other American. How does that sound?
Ever consider the idea of dual timelines existing side-by-side? I this setting the Twilight war both happened and did not happen. Something happened in 1990 Russia during the coup. In one version Boris Yeltsin was killed and the coup plotters succeeded. The Soviet Union was still in decline afterwards but went out with a bang rather than a whimper taking the United States with it. The Twilight War happened as did the the original 2300 timeline. The other timeline is our timeline up to 2003, this timeline gets vague between 2003 and 2050, but by 2050, the US and several other nations have colonies on Mars. By 2100 a unified Martian government forms. Perhaps the war of terror continues as well. By the time 2300 rolls around the world looks different from the old 2300. In both timelines the stutterwarp engine is developed. the barrier between these two universes is somewhat thin. Perhaps certain events can lead to a transfer from one timeline to another. The Stutterwarp for example when not working properly might cause a transference from one universe to the other. Certain ancient artifacts discovered on unexplored planets might cause this transference. Perhaps time travel from the future was involved in changing the timeline. A visitor from the Future might have either caused World War III or prevented it. Perhaps a third campaign could evolve between competing Time Travellers from different time lines. One could be French and the other American. How does that sound?