Great ideas.
I completely forgot about leghorns!
They are PROLIFIC egg layers, the males can carry a bit of meat, they are excellent foragers, they are very flighty (can fly away from danger), and very slim, quick birds. They are not "semi-feral" or even close to feral for that matter, but...
@chickfused mentioned they need dual purpose breeds that are also cold and heat hardy.
I thought of that, but my game birds don't have much meat on them, and don't lay much eggs. I do agree that Barred Rocks and Wyandottes are pretty slow.
A breed known to fight is an Asil. They are a fast...
Birds that I have found "Semi-feral" while still providing eggs/meat, AND are cold and heat hardy include Barred Rocks and Wyandottes.
I don't think you can get a specific breed that "pretty much sustain itself" on any land. Predators come, and some predators are no match for chickens, even if...