That's political, however, rather than technical. As one example a combination of Korea going hot again and China wanting to maintain a buffer state at all cos

That's political, however, rather than technical. As one example a combination of Korea going hot again and China wanting to maintain a buffer state at all costs. Vietnam wasn't all that long ago, and there's no really good technological reason that couldn't happen again. We're also reaching a technological stage where it doesn't necessarily take two superpowers to fight a proxy war. Could India and Pakistan fight a proxy war without superpower involvement with a substantial air war component? Technologically, sure.