Ah yes, I misremembered: there's an additional slot but a very specific spec requirement. They'll be whitelisting individual devices.

I don't think it's been confirmed whether they'll be enforcing a whitelist, or merely publishing a list of drives that have been verified to be compatible. The latter seems more likely to me, simply due to the sheer volume of SSD models that will meet the technical requirements. (Especially where we'll see a dozen or more brands selling the same hardware with a different label.)