[morid1n]

With the T2 chip which is already present in other Macs. It’s optional at the moment but I assume at some point it will be closed off. And then there’s the ARM CPU argument - we could get those soon.

[slantyyz]

According to a Linus Tech Tips video[1] that I saw a a couple of days ago, you can use PCI nvme drives on the new Mac Pro, but it won't even boot unless one of the proprietary Apple SSDs is connected (because of the T2).

[1] https://youtu.be/mIB389tqzCI?t=180

[morid1n]

You should be able to turn off the T2 function Secure Boot which blocks booting from other drives: https://support.apple.com/en-us/HT208330

[slantyyz]

According to this newer Linus Video [1], one of the T2 SSD slots still needs to be populated with an Apple drive to boot from other drives.

[1] https://www.youtube.com/watch?v=zcLbSCinX3U

[derefr]

Which makes sense: it needs to load firmware/EFI from somewhere; and in a setup where you expect your own SSD to be a fixed resource in the system, there's little reason to have separate BIOS flash.