

It won’t kill commercial banks because there’ll be limitations. Biggest is you won’t be able to take a loan from the central bank, which is the largest slice of the pie for any bank making money. They can also put other limitations, such as no non-EU transactions, or having a max limit per month.
Not all your money. Most people have more than 1 bank account. So this won’t change that. Also SWIFT transfers also include international transfers, and most people aren’t doing that outside of rare instances. Digital currency is only within EU regions, so this solution won’t affect non EU transfers. As OP said the goal is to reduce commissions to Visa and Mastercard.