Assuming energy consumption isn't a factor, I'd just get some U.2 or U.3 2.5" drives for my system instead these days. They've come down quite a lot in price.
You'd have two options:
1. Connect them via cables to motherboard connectors or bifurcation/switch-chip PCIe cards or
2. use a PCIe bifurcation adapter card where you can directly mount them to (50$ iirc).
If your motherboard slot doesn't support bifurcation, then you can only attach one drive per slot or you have to get a PCIe card with a switch chip on it, but they are expensive.
The drives come in 2.5" format and you can, if you use cables, mount them in HDD/SSD slots of your pc case in front of case fans. Just ensure that they have proper cooling, i.e. there is enough space between drives or the fans have enough static pressure, and you're good.
If you mount them on the adapter card, make sure a case fan is blowing alongside their surfaces.
Sometimes I can get them for lower prices than their Desktop M.2 counterparts, which have much lower endurance, no powerloss protection, less sustained performance, etc.
One downside: They don't have deep energy saving power states, because latency is all that matters for that kind of hardware, meaning they'll use 5-10 Watts idle and under load up to 25-30 Watts. This is the reason why you need adequate cooling.
Also this is the only way I know of that you can get the full sustained read/write potential of SSDs, because even with a good heatsink, you can never remove that kind of heat from the chips fast enough if mounted on the motherboard.
Example:
Micron 7400 PRO - 1DWPD Read Intensive 3.84TB, 512B, U.3
270€, new, incl. 19% VAT (newer model with somewhat better values is available, but the differences would be irrelevant to me)
Reading: 6600MB/s
Writing: 3500MB/s
IOPS 4K read/write: 800k/150k
Endurance: 7PB (standard/mixed write workload) or 25.7PB (sequential writing)
Notes:
I would never run any of these enterprise drives, even if they sometimes come in M.2 format and you attach a heatsink and have fans blowing on it, as M.2 unless you have the kind of airflow that is typical of enterprise rack servers. They just get too hot.
If you compare the stats above to M.2 desktop drives remember that the values advertised are quite different. When they say 3500MB/s write speed, then they mean that it can be sustained more or less indefinitely for the entire drive. These are not the inflated burst speeds of desktop SSDs, where the performance tanks when the cache is exceeded.
They switched the pins from U.2 to U.3 standard. You can plug U.2 and U.3 drives into U.2 slots, but you can't plug U.2 drives into U.3 slots.