The debate over socialist "central planning" vs. capitalist "markets" is meaningless and distracting. As I noted earlier, the best we can say about this choice, absent specific concrete problems to solve, is that we should centralize what is better centralized and distribute what is better distributed, and apply careful engineering principles to making everything fit together. But in order to solve these concrete problems, socialism requires deeper and more radical structures: transparency, democratic accountability, and radical income and wealth equality.
A socialist economy must be transparent, both when centralized and distributed. Any person should be able to figure out what any part of the economy is actually doing and how we justify doing what it does the way it does. We need to be able to see all of the decisions that economic institutions are making and see all the data those institutions are using to justify their decisions. (We cannot ever see the real reasons why specific people make specific decisions; we can see only their stated justification.)
We need to see exactly what the government is "centrally planning" and why, and we need to see exactly what "distributed" individual firms are doing and why. This information needs to be directly available to anyone and everyone.
We don't need individuals' specific purchases to be transparent. Individuals need privacy. Nobody needs to know that Floyd Abernathy of Peoria likes peppermint toothpaste. We need to know about purchases only in the aggregate, and we can get that information from producers and distributors, who do not need privacy.
Now that we have the internet and very good storage and searching technology, near-absolute institutional transparency is technically feasible. Everything the government does is on the internet. Every firm's books, policies, procedures, and technology is on the internet. We do not need trade secrets and proprietary technology: we want good productive technology to spread as quickly as possible.
Second, we need democratic accountability. Democratic in that each person has the same amount of political authority ("one person, one vote"), and accountability in that the people themselves, acting democratically, has sovereign authority over economic entities. If the government is doing a bad job of central planning, if some firm is rent-seeking or slacking, the people, acting democratically, need to be able to address the problem. And they need to address it not two years from now, when the next election rolls around, but today.
Democratic accountability poses a more difficult technical challenge than transparency. It is not feasible for even 100,000 people, much less 300,000,000 or 7,000,000,000 people, to vote on every issue of social coordination that affects any given firm or locality. That's not because we lack the technology (we could securely poll 7,000,000,000 people a thousand times a day if need be), but because even with transparency, individual voters do not have the time to build an informed opinion on every individual facet of the economy of even a medium-sized city, much less a nation or the world.
However, as I've written at length earlier, delegated democracy can approach the requirement of truly democratic accountability.
These first two requirements should be relatively uncontroversial relative to the third requirement, radical income and wealth equality. Just as political democracy requires one person, one vote, economic democracy requires "one person, one paycheck": every individual has the same demand on the social product.
This requirement requires more examination, so I'll write more on the subject later. Briefly, though, the goal of communism (at least as Marx seems to have thought about it) is a society where the material requirements for not just life but a comfortable, dignified, and civilized life are as ubiquitous as oxygen, with as little need for specific accounting and rationing. When and if we have an intermediate socialist society, we can move towards a truly communist society only by equalizing the demand on the social product. Only then will we eliminate the economic incentive for individuals to exploit others, and create a social incentive for every individual to have more.
Our society must decide what should be centrally planned and what should be distributed, we must make these decisions about specific concrete economic and social problems that arise, we must decide democratically, and we must make these decisions on a level economic playing field.