A no carrier phone was possible before, but not in the same way being discussed by Purism. (I guess when google offered VOIP numbers that would count, but I’m not sure about how you registered for those numbers.)
Librem Dail will give you a number, I’m guessing, that will work with normal telephone systems. This is a big difference.
Outside of this, yes, you could today, just buy a data sim card, and not have a phone number on your phone. You would then use VOIP apps for calling. Would work pretty well already. With what Purism is proposing it would work even better, and would be a great solution.