I realise that you have never been an Electrician, but if you had have been then you would probably be tired of people phoning about such-and-such a circuit breaker not working (because it's not actually connected to anything). It leads to unnecessary confusion.I missed that (although to be precise, you didn't specifically state that you expect to see DIN rail-mounted blanks, you said that you hate non-DIN rail-mounted ones, but I take the point that you wouldn't install the clip-in ones).
But that still leaves the customer with a storage problem created by you, and (probably) extra costs created by you. I do struggle to see how that is a better and more professional practice.
In my experience most Electricians consider it bad practice and far prefer to see blanks used. (As said, I don't rate non-DIN rail-mounted blanks at all - some may even fail on the tool or deliberate action required to remove them.)