Why do you think those would make it more effective and why do you think the US isn't a planned economy?

I don't think any economy should be either/or. Things where you can't really have competition, or just plain don't, or are just to darn important. Should be state run. Healthcare, education, utilities, infrastructure for sure. Even things done in the private market should be well regulated. You also need a populace where the average have a decent amount of discrecionary income as they need to make decisions on what best to buy, not what they can afford.

Yes, 100%. Look into cybersyn and what it was able to accomplish with its highly limited means. Technology since 1991 alone has progressed massively and would be a far more effective tool for organizing a economy that meets peoples needs than the soviets ever had access to. They took a 90% feudal society to fucking space in 40ish years and they largely did it on paper.

To be clear though. Planned economies already exist and function quite well on these systems. They just aren't working in your interest. Verticle integration is a planned economy. Corporations organize their planned economies quite well and the work already done could be applied far more effectively to provide for people. It's just not what those systems are for under capitalism.

Viable is a binary yes/no condition, so not wouldn't be more viable. It was viable then, it's viable now. But the new tech would absolutely make it easier and more effective.

All of the failures of planned economies are because leadership ignores the data they had and having more isn't going to make them listen. The problem was never the data.

A fully planned economy? Probably not. You could probably get a few key industries, but a country is a lot more complex than a corporation.

Even with better computational tools, you have to worry about the interface of those tools. Who determines the priorities of different commodities? If AI, who trained the AI and what data did they use? What happens when operators fudge numbers for one reason or another? What happens when projections differ from reality?

An economy is complex and dynamic. Simple, straightforward industry and administration can use modern tools to operate more efficiently. But I don't think we can construct a system which collects data accurately enough to make useful conclusions across the entire economy. Even with the best computer imaginable, garbage in garbage out.

And even if you could perfectly collect necessary data, you've just built yourself a perfect surveillance state.

China seems to be doing well?

It makes the most sense for natural monopolies like oil and gas pipelines, power grids, telecom, rail, post, meat packing, food distribution. Etc i personally think all of those should be state run enterprises. Competition adds needless waste when the very nature of each industry forces a single winner. Competition is an unnatural state that has to be forced through anti-trust laws.

Definitely, there's absolutely a place for central planning and state run enterprise.

Exactly. Some services are natural for commercial entities. Things with high consumer elasticity, low barrier to entry, and a lot of competition. There are things that are better governmental or well regulated monopoly or near monopoly businesses. These are things with low elasticity, high barriers to entry, and no or low competition. There are also things that governments have low risk when investing, and where competitive organizations have high risk when investing. Anyone of things one specific model best covers everything is delusional.