If I were in a position of authority I would propose a gradual transfer of power from the private sector to a national central bank. Something like an increase on the fractional reserve ratio for all private enterprise by 2% per year until it hits 100. "New money" should then only be lent out by the central bank through private institutions acting as brokers. Profits from loans then go into the public treasury. Interest rates can then be controlled by a central authority who's core interest in is the welfare of the people, rather than shareholder profits. Periods of increased economic growth would result in increased social and public infrastructure spending, while periods of slower growth result in higher rates that help deflate bubbles and encourage saving.
There are fundamental problems with this scheme. The first is that a central authority is always far more subject to corruption than a large number of smaller entities. In many ways, centralizing things simply makes a bigger, easier target for the predators out there (some of whom usually end up in control of it).
The second is that no central authority knows what is best for the people. In many cases, nobody knows what's best. The world is a complex place, and there are many different viewpoints. A decentralized system has advantages here.
These will remain fundamental truths for the foreseeable future, and thus no central authority can be trusted to look out for the welfare of the people.
Humanity has had a really poor track record with central authorities. Study 20th century economic history for the gory details: there's the Soviet Union, India, China, and many smaller countries that have tried the central authority scheme and failed.
Further, you'll find examples on a smaller scale in the history of many countries, where bureaucracies functioning as central authorities, with respect to some particular economic aspect of society, have also failed to look out for the welfare of the people. Consider the history of water development in the USA, involving the US Army Corp of Engineers and the Bureau of Reclamation, for lots of examples of how central authorities go wrong: Marc Reisner's Cadillac Desert is a good introduction to this.
Similarly, we can see many examples of bad decision making in the history of large corporations: the executives in these organizations make a lot of really bad blunders because the organizations are too big and the executives too out of touch with the reality of their business (refer to the industrial psychology literature for examples). Any centralized authority will have the same kinds of problems.
Further, if you follow the history of invention and discovery, you'll see that a lot of things that ended up being really useful and important weren't predicted in advance. Having private access to funding is an often underrated benefit of the decentralized economy.
The outlook for any scheme involving massively increased central authority is dismal. There are better places to focus one's energy for those concerned with improving the public welfare. A vastly simplified tax system -- one that was truly progressive instead of just pretending to be -- would help a lot for nations like the USA. Cleaning up corporate law would help a lot as well.