I'm fairly certain a lot of people have spare NVMe SSDs of varying capacities, as one upgrades or accumulates more from sales. Modern motherboards don't have enough M2 slots to accomodate all of these drives, so they're not being put to use. And I don't think they have figured out to put the M2 connectors sideways so the drives can be stacked similarly to RAM. But what most existing motherboards do have is a lot of SATA connectors. My x570 has 8, and both of my itx b550s have 4.
So what I would like, would be an enclosure that is the same exact size as a 3.5" HDD that will fit inside of drive bays of a PC case. A 3.5" HDD draws 6-10W, and peaks at 25W. 2280 is about 5.5W, less while idling. So one SATA power cable should deliver enough to power all four SSDs. And it wouldn't require having to use an electrical plug, like every 3.5" external enclosure requires. I would like for it to connect to and use 4 separate SATA data cables as well. No software, no compability issues with mixing PCIe, all drives are individual. This would free up the USB ports that external enclosures require. It wouldn't block fans like PCIe adapter cards. It would be the same speed as existing USB 3.0 enclosures, so the 550-600 MB/s limit isn't an issue.