You can fill it with SSDs, and SFP28 is so common the prices are cheap:
https://www.fs.com/c/25g-sfp28-3215
But no, spinning disks won't saturate it, even if you were doing 100% sequential reads.
(I originally said fill it with NVMe - I was wrong)
It looks like you can put 2 nvme drives in it, for caching.
It looks like you can put 2 nvme drives in it, for caching.