A:Answer It has 2 expansion bays located and n the bottom of the case when you open the access panel. Would you be able to make this your primary drive? I would advise against it, the Optane Memory is not so merging you want to tinker with, it’s very finicky, also you would have to clone the OS over to the new WD 4tb drive, which can also get messy.
TL;DR You can use that as a secondary drive no problem with the extra expansion bays, I would not try and use it as your primary as that makes a mess of things.