So far, the ECB says that virtual currencies should not be promoted.
This is not banning, it is merely to say that they do not want banks to have anything to do with Bitcoin.
To ban Bitcoin, they would have to make the trading of a non-currency asset against money illegal. Difficult issue, as you can trade digital goods of any kind.

Or they would have to interfere with bartering, i.e. the exchange of one good against another without the use of a currency.

One or another - adressing the topic would probably involve a massive effect on other legal topics in the finance sector. Nobody wants to get their fingers burned on that. Plus the ECB would stir up a lot of dust for being anti-innovative. And some banks are playing with blockchain-stuff themselves.

From the article cited, I would assume that they are pretty clueless. Yes, they would like to regulate virtual currencies. They do not like it. And by now, its considered relatively harmless.

But so far, I do not see, how they want to do it.
European law / finance specialists anywhere?