I've noticed there aren't a lot of reasonable home/sb m.2 NVME NAS options for main boards and enclosures.
SATA SSD still seems like the way you have to go for a 5 to 8 drive system (boot disk + 4+ raid6).
I don't now if you consider it "reasonable" but the Gigabye Aorus TRX boards even from 6 years ago came with a free PCIE expansion card that held 8 M2 sticks, up to 32 TB on a consumer board. It's eATX, of course, so quite a bit bigger than an appliance NAS, and the socket is for a threadripper, more suitable for a hypervisor than a NAS, but if you're willing to blow five to ten grand and be severely overprovisioned, you can build a hell of a rig.