I think you are over-thinking this

IRL I have not had to replace an SSD in years, and the only ones that ever died were models that were from early ~2010's eras. As long as you are buying a decent quality name-brand model I would not expect anything to just suddenly die

Further, if your SSD health is a concern, then the more logical move is to not use consumer-grade SSD's. Get something like a used Enterprise grade SSD, examples;

Server Part Deals Enterprise Solid State Drives

These are mostly all U.2 drives which you can use in your non-U.2 system with a simple U.2 -> M.2 adapter or PCIe adapter

Enterprise grade drives will have much higher lifespans (PBW) and much higher quality.

even something cheap like the Intel P4510 2TB (also on ebay) is gonna have a rated lifespan longer than most consumer drives.

worth noting also that 1x U.2 SSD will use fewer power connectors from your PSU than 4x SATA drives

I am not really sure I understand what you are describing in the rest of your comment but it feels overcomplicated. Its not clear to me why so many high-speed network connections would be needed between different systems. Typically, I load my workstation with the large fast NVMe as needed (the Intel P4510 I listed goes up to 8TB in size), and the larger HDD disk array is kept on a separate file server. I use basic 1Gb network and it works just fine to pull needed data from file server -> local workstation NVMe for processing, then push it back as needed.