I disagree, at issue is human nature and bad judgment. Even the most basic ideas can be acted on in a good way and in a destructive, dramatically different way. I'm with Vallen, that logic rules out any idea if we were to fully carry it out.
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A third season is a horrible idea. I want to be clear, there is no reason they can't finish this in 50 episodes. 18 episodes is plenty of time for LeLouch to rally the world and take the fight to the Britannian mainland. If it goes longer, it'll be very dragged out. And it will suck because that extra time won't be used to focus on the world, it'll be spent on even more of LeLouch's introspection and obligatory breaks for fanservice. We don't need more of the same.
Geass isn't a war epic and will fail if it suddenly tries to be one. There isn't nearly enough actual war in this show for it to be called that. It has always, always, always been a character driven series with a mix of mecha warfare and silly fanservice supporting the whole thing. It doesn't have the political depth of Gundam 00, let alone LoGH, which trumps everyone in that department. LoGH covered more plot than Geass could ever hope to, and built up backstory throughout the series.
By all means build up some context beyond Japan's sad story, but it is way late in the game for Geass to suddenly tell us more than we'd ever want to know about China, or Europe, or what Todo was like fifteen years ago, or what kind of wacky adventures LeLouch and Suzaku used to have as kiRAB. There may be some good stories there, but none of that is relevant to the story that's being told. This is the tale of LeLouch's rebellion, and they'd be well advised to stick to it.