I’m looking at the future and what might be good replacement that offers a blend of power-efficiency, flexibility, and storage cost.
Any modern CPU will improve energy efficiency. AMD AM4 platform and Intel N100 are very cheap. AMD SP3 platform is also very cheap and has a ton of PCIe lanes and memory expandability for gpus, NVMe, and running lots of VMs.
For storage cost, used hdds are currently $8/TB, generic NVMe is currently $45, and used enterprise SSDs are $50/TB, decide which you want to invest in depending on your needs. Used enterprise drives will be the fastest and most durable for databases and RAID.
https://www.ebay.com/sch/i.html?_nkw=pm983+m.2&_trksid=p4432023.m4084.l1313
SSD prices are expected to decrease faster than HDD prices, and will probably overtake HDDs for value in ~5 years.
About dGPUs, Intel A310 is the best transcoding Gpu out there. Used Nvidia datacenter gpus probably have the best vram/$ and pytorch compatibility for AI
LVM is a good way to do raid on linux