It is worth pointing out that the investment is chump change and that the investment would be highly profitable. Say bitcoin replaces all card payments in the Euro area. That is about 54.8 billion Euros in 2008. Suppose that the average fee on bitcoin payments is 0.1%. Suppose that hardware depreciate at a 20% rate [slow for computer hardware], that labor costs are negligible [labor costs make monopoly easier], and that the interest rate is 5%. Assuming a competitive market, we have

capital rental costs=flow of bitcoin payments
(0.20+0.05)K=0.001*54.8 billion
K=$212 million.

It is chump change for a large corporation like VISA (let alone the central bank). More importantly, monopoly control easily repays itself. Suppose the monopoly raises the fee to 3% (same as credit cards) and that the volume of payments declines by five-fold to 10 billion as people flee instantaneously to gold or other types of rocks or whatever you might think of as 'sound money'. VISA/ the central bank will earn $300 million from the 3% fee. That is a nice 142% return on capital.

Now let's think about the volume of payments decreasing five-fold in one year. Is that plausible? Of course not. You cannot bootstrap a new currency in one year. If you could, you guys would not still be using USD. Thus the monopolist's profits during its first year of operation will be far greater than a measly 142% annual rate of return.

You may say we will have many competing PoW currencies. If so, the payment flow from each of these media decreases accordingly. The central bank's total expenses for controlling many small competing cryptocurrencies are identical to the central bank's expenses for controlling one large cryptocurrency. Only the total flow of fees matters.

Why don't you propose a fix for the problem? Or explain why I am wrong? Why does burying your head in the sand seem like a good idea?