This isn't new, the Mac Studios and Mac Pros use similar proprietary modules. Apple even sells the Mac Pro modules separately so you can technically upgrade the primary storage in an officially supported way - for a ludicrous mark-up of course.

https://www.apple.com/shop/product/MR393AM/A/apple-2tb-ssd-u...

In practice if you have a Mac Pro you're better off just getting a PCIe SSD instead for a fraction of the price. Retail for a very fast 2TB SSD is ~$150 while Apple wants $1000.