In reality this statement implies a broader concept: "If the Bitcoin becomes a widely used financial instrument, the bubble will not burst".
In fact, there is the possibility that Bitcoin can become a widely used financial instrument even if it could never become a transactional currency (or, as Carlo Piana says, a currency: a currency to make daily payments, like the Euro). In particular, Bitcoin is a reserve of better value than the Euro: if this were its role within the (new) global finance, the previous statement could be true, and the bubble could never break out. Therefore, there is no need for it to become a currency: the important thing is that it takes on a specific role as a financial instrument, regardless of what role it is (transactional currency or reserve of value).
But why Bitcoin could be a reserve of better value of the Euro? (Currently it is, but we do not know if it will still be in the future).
The Euro is an inflationary currency. That is, the objective of the European Central Bank, which issues and manages it, is to keep inflation around 2%. In particular, the Euro must not be deflationary, because deflation increases the real value of debts (even if the nominal value remains the same), and given the immense amount of debts in Euro if there is a very high number of deflation in this currency of debts would become unsustainable (starting with public ones). So the Euro can not and must not become a deflationary currency.
However, the inflationary coins have a downside: they inevitably lose value over time. In other words, even if their nominal value remains unchanged (50 euros are always, and always will be, 50 euros), their purchasing power decreases (due to the increase in prices). In fact, we recall that "inflation" means nothing more than price increases, so the ECB's objective is to maintain an average price increase in Euro of 2% per year. This in fact inevitably depreciates the Euro by about 2% per year. Therefore, keeping Euro still in the bank account means losing about 2% a year. This is why the Euro is not a good value reserve at all.
Bitcoin instead was created to be deflationary. That is, it was created to have an issue of new currency controlled and even limited in time. Every 4 years the coin issue halves, and in 2140 it will cease. Since inflation is generated when too much new money is injected, the fact that the emission of new BTC tokens is controlled and limited in time generates the opposite effect: deflation.
Therefore from this point of view Bitcoin is the exact opposite of the Euro: it is not suitable for debt, but leaving their tokens "firm on the bill" not only does not create loss of value, but even increases it! In other words, it is (currently) a reserve of better value for the Euro.
If things continue to stay that way (ie, if the deflationary nature of Bitcoin turns out to be solid and permanent) it will not be enough to keep Euro on the account as much as it will hold BTC token token. At that point the role of Bitcoin will be clear: it will become a reserve of value in place of the Euro (or traditional legal currencies, called "fiat"). If this happens, the bubble will never burst.
