Well, pci-e 2.0 x16 is good for 6GB/sec... that's pretty substantial... you could get 4 lower speed drives and stripe them easily.
It seems to scale them well too.
Amfeltec Squid x16 PCIe board + four SM951s
6GB/sec in a single slot is pretty epic. I have 4 slots dedicated to get 6GB/sec right now...
So... someone actually did it...Oops, you are right! Thought that was just a better price for the link below. Here is the PCIe 3.0 version
PCI Express Gen 3 Carrier Board for 4 M.2 SSD Modules (SKU-086-34) ($609.00) : Saelig Online Store
Costs just a lil more for the card, but worth it.
$609 for the board
$199 each for 4 MyDigitalSSD BPX 80mm (2280) M.2 PCI Express 3.0 x4 (PCIe Gen3 x4) NVMe MLC SSD (480GB)
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$1405 Total
10.4GB/sec
5.6TBW wear life
5yr warranty on drives
73 cents a GB!