They were. The connectors at the end of the drives were different and that was all (adapters were common, probably still available)

There's also scsi 3.5" drives out there. Some ThinkPads had them. In fact, those drives were 2.88MB, just like on the NeXT, the 1.44 was common but one of a large number of capacities in that form factor...

If you do this, use dd, not cat. Why? dd has this

noerror continue after read errors

You're going to get errors. Lots of errors! However, 80% or so of the time, most of the disk is still recoverable, but only if you use the right tools.

It's going to be slow, real slow. A few minutes a disk with errors.

Now that I think of it, you can probably swap the NeXT and thinkpad drives with a little effort. I bet there's a good arbitrage on eBay here if I'm right.

There's systems that go the other way, sd card/usb disk to fake floppy but what I really want is usb to fake floppy. In this model the usb exposes itself as a configurable given capacity drive on both ends of the pipe, fake on both ends

At the modern computer I copy over the files to the fake drive disk by disk and on the old computer I tap enter accordingly. Then someone can do a 20 disk install or whatever without a bunch of effort. It's not a hard device to make but i checked and i still don't see it