It hasn't gone away, though. Just last week the news in the US covered a new law that went into effect here that prohibits companies from discriminating against people because of their genetics. While the issue has gone to the back burner the last five years or so, it hasn't really gone away. As to climate change and new fuels being more relevant, I don't see them any more or less relevant than Genetics. The current relevant thing going on is the World recession/depression and war and both SEED and 00 cover the war aspect, while the World economic issue isn't touched on all that much in either show (and I'm not sure I want to see a Gundam AU that is "Gundam, the Economic Universe" anyway )
As to Destiny, you hit one of the big things that did irk me about it. I often wonder if Fukuda and his wife either had someone holding them back during SEED that wasn't with them on Destiny because the reasonably even handed look at both sides very much was missing. Instead we get a show that was clearly meant to be a political thesis on the evils of capitalism and the West and how Marxist/communist style single rule government was the way things should be, aimed at the viewers in Japan in a attempt to sway them to their outlook. Which is why I think things did melt down at the end. IMO, what Fukuda and his wife were going for with Destiny was that Durindil is the good guy and the Destiny was suppose to show people the foolishness of the Orb/Archangel crew/Kira & Lacus's position on things (Fukuda and his wife were fairly open in interviews as mentioning they held marxist views in interviews and I think Destiny makes if fairly clear their dislike of capitalism and the West in general). I think Destiny was a attempt to turn the entire SEED story on its head and do something new and daring in their eyes. The problems with what they were trying were first, the Japanese viewership not only rejected/didn't get what they were going for but demanded that Orb/Archangel crew/Kira & Lacus's be returned as the main emphasis of the show. Rightly so IMO because this was suppose to be a sequel to SEED, not a turned on its head re-telling of the story. Second, they didn't do a good job of telling the story, period. They barely wrote beneath the Ham Fisted level and drained SEED of its depth to push their agenda.
Third, not all the writers, and I have a feeling most of the rest of the staff, signed on to do this take on the story (I have to wonder if they explained any of this to anyone or just figured they'd slip it under TPTB at Sunrise and the TV network instead). Unfortunately for the viewers those in charge over Fukuda didn't figure out what Fukuda et al were up to until about twenty episodes into the show. Even then, IMO they didn't figure it all out until around fifteen episodes from the end. At which point they seem to have stepped in and tried to re-adjust things drastically which lead to the wackiness because Fukuda was still in charge to a point and everyone was fighting with each other. [And still, Fukuda may have had the last laugh with the Lacus looking like the Emperor from Star Wars stuff at the very end of Destiny because why do that if you don't think Lacus is the bad guy? (then again, why turn a character you made out to be the good guy in the first place at all? I really do wonder at times about the sanity level of the Fukuda's during the making of Destiny ).]
So that takes us to the here and now. We have two Gundam universes in the last ten years and I'm not sure either is truly better than the other. What they are is different from each other and wildly different at that. I think unlike Gundam Wing and Turn A Gundam these show both have potential to do more in their universes (those two might as well, but I'm sticking to the 2000s). Destiny was a mess but IMO it wasn't a mess to the point it ended everything. Heck, I don't even think you'd have to toss Destiny out - they left things at a point they could tweak themselves out of it, san the issue of the "people who died that probably should have stayed dead" issue which is more of a personal taste situation as I see it (personally the fact you can't keep Tiera and Co (I'm blanking on their group name at the moment) from 00 any more dead than Mu, Kira, and Andy just as silly). They just need to replace Fukuda IMO and then try and get back to the more even handed storytelling used in SEED (bring back a deeper plot verse a agenda). I want to see more SEED, you and others want to see more 00 but at this point we're getting more UC universe instead. At this point I'm not sure the biggest obstacle to getting more CE or AD Gundams is economics verse lack of potential new material. I think both shows have a audience in Japan, along with the original UC, but finding the funding to do them is going to be the trick (currently the universe with the biggest economic pull is UC because its fans are in their 40s and have still have buying potential verse Japanese twenty somethings who are often struggling to survive these days).