I'll say what I've said before about this but please don't let it ruin your enthusiasm.
We don't have the source code so we can't change everything freely. To solve this, we'd need to start from scratch like you're describing. It would have to be on a new engine since I doubt we can get a UE2 license. While ELiZ proves things can be ported in both directions (newer to older, older to newer), that's just assets. We would have to re-code the core parts of the game. Sounds great and we could probably get a team together to do it but there's a catch; It won't have the same feel as AA2. Never will. Even the AA devs themselves with all the source and just moving up engine builds in UE2, they couldn't keep gameplay the same. Everybody has their own favorite AA version. When you think about writing all new code, you're talking about building an entirely new game that doesn't have appeal from the AA2 audience. You're then talking about competing with all the other shooters on the market. Look at ARMA, Battlefield and Call of Duty, they each have their own niche market and nothing will ever compete with them. Building an AA clone would directly compete with ARMA. There's another game that has been on Kickstarter that pretty much is an AA clone, aiming for small-scale realism. There just wouldn't be any room in the market for competition, at least not without a paid or promise to be paid and dedicated dev team with no speciality gaps.