You still have most of the power concentrated within the developers, pool owners, and exchanges. This has resulted in major instability due to some of these major players operating effectively scams via either outright stealing or the hiding of major losses.

Most of the issues with currencies(and most everything) is trust and the motivations of other people. Technology might help democratize a world currency, but those who corner the market first will have major influence over it, which in turn will quickly result in the same imbalance in power which was trying to be avoided.