Oddly enough, I bought a bunch of M.2 format adapter things from the overseas fleamarket. One includes 9 SATA ports in a 2280 form factor. I've also seen PCIe x8/x16 expansion boards that connect via M.2.

If I had transfinite funds, I would make a video about turning a dual socket motherboard+CPU combination with the most PCIe lanes with the goal to connect maximum GPUs via Thunderbolt 4 hubs and enclosures, PCIe bifurcation cards, and M.2-to-PCIe adapters (whichever method maximizes GPU count) all powered by many PSUs.