Socialism under old labour was the closest you'll get. Any state system without accountability, or in other words democracy, will get out of control sooner or later. Labour knew they had to compete with the conservatives come election time, and did what they could to keep popular and the state working. But ultimately the system couldn't be sustained because ironically British socialism was supported by American marshal plan money.
A socialism experiment on a global scale would need a colony on a new world to be tested in conditions that wouldn't lead to its ruin. It can't compete with capitalism. That or the advent of nano technology or something equivalent that would allow everyone to agree that the state can take ownership of all industry, and let people do as they like. The older premises of marxist socialism are extremely obsolete, beyond some vague notions of struggle and economic inequality being bad, 1850s ideology is just not integratable into the early 21st century. It's why old labour failed. If you think something more extreme would work, I'd say the evidence suggests that it'd fail harder before long.
The only possibility where I see it working long term is on a colony on a planet lightyears from earth where there's no alternatives to compete with. Even then, utopian socieities begin to unravel when they realise what happens in the outside world; the Spartans are one example of that. "They have that there!" may be enough to slowly erode the very fabric of a society which on face value seems pleasant and balanced enough. For socialism to work effectively it needs a genius planner, and I mean a genius. Not marx, not Lenin, not Atlee, no one like that. Someone really, REALLY clever. And right now, no one has stepped forwards given the challenge. I wonder if someone ever will? Otherwise it will just lead to the boom and bust of socialist planning, just like the boom and bust of capitalism. The problem however, is that when socialism has a bust, it cripples the system.


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(it is an accurate description of my politics, but for most people in the US "libertarian" and "socialist" are contradictions).