I'm a fan of T2000 variants - the version of t2000 I'm going to play with my players is actually closer to The Postman (cynically, the movie rather than the book....as the latter is just a bit too way out there...more on that later.) and Jericho (the TV series with Skeet Ulrich). I'm honestly more interested in that side of things than wandering round Poland. I'm chewing the idea of bringing in stuff from The Morrow Project and Living Steel to create an ongoing narrative framework. Both games had the idea of being part of a rebirth. I think there's real mileage in a "Darkness before the Dawn" campaign. I'm titling mine "Nor Gloom Of Night".
Some other variant campaigns -
Before The End - honestly, catch the Jack Ryan series on Amazon Prime. The first story (with a dirty bomb in the US) is great. And if the players were involved in stopping or even failing to stop the disaster, it would, it could be gripping.
Alien invasion - a roleplaying game I really enjoyed reading years ago was Domination by Starchilde Productions (the roleplaying part of Sabot and Laser). It's a military focused game that has to deal with a contemporary invasion by a militarised alien force (The Kalotians) and their allied and servitor races. The odds are horrendous, the possibilities huge and then there's the concept of earth soldiers being recruited as a servitor race to go menace another planet. There's some optimism as "V" would show us, and even being sent to another planet has some worth, if the players are recruited with the promises their families will be catered for.
Either of these two stories would be interesting to me, but the specific mention on Domination has most appeal. I never got to play it, but I saw the books (two or possibly three?) in my local games shop as a teenager and recently looked them up again. Something along those lines, but with more up to date rules and an expanded background would work really well (IMO) and I'd love to be able to convert and expand on the original material.