Are we sure those digital currencies would be handled directly and fully by the central bank at no (direct) fee per transaction? Who's to say that the way things currently work won't stay exactly the same, except for your Visa card being denominated in dEuros instead of Euros?
I may be a pessimist, but the way I see it, the current end-user facing financial system (retail banks and payment processors) are much too big and much too greedy to stand idly by while the central bank takes their pie away.
The current state of merchant banks and payment providers can very well continue, without CBs having to assume new responsibilities.
After all, the trend is towards more privatisation, not less.
I share your pessimism. I'd say the central bank is the oven wherein the commercial banks bake their pies.
I personally have absolutely no problem with them and I'd be very glad if I could settle every transaction with a digital Euro. I don't particularly enjoy the middlemen in the form of countless payment processors who all take cuts out of transactions, and I don't really see what privacy or tracking burden applies that existing firms don't already engage in.
To me the payment infrastructure consisting of countless of private firms seems more like a relic of the past. Free, instant financial services to me are ideally a public utility in the same way the water or transport infrastructure is.