The argument about using a credit card is meh - it’s all software at the end of the day, there is no reason why I should have another card, an account with another (legacy) company, etc just for the off-chance I make a large purchase if Monzo can do it.
If Monzo does this right (it does need a way to arrange the loan in advance though) it will eventually negate the need for a credit card which seems like a good thing to me.