MBPs haven't had a "hard drive" to solder on in a few years: the "T2" security chip is also the SSD controller, managing the "freestanding" flash chips (which are soldered onto the board). The SSD isn't a separate thing at all.
That, however, does not prevent the flash chips from being removable. Sure you would not be able to access the data, but could replace/upgrade the flash without throwing away the computer when they fail. In fact that exists in a real T2 product: Mac Pro. You won't be able to replace it with off the shelf NVMe though.
