M.2 SSD Compatibility in WWAN Slot

From what I can gather, the WWAN slot is mini-PCIe with an M.2 B key connector (since the modules have six pins on the end instead of five). Will a SATA M.2 SSD with a B+M connector be compatible with this slot? I can't determine if the slot supports SATA. I also find it very difficult to find a mini-PCIe M.2 SSD with the B key connector -- instead they all have the M key connector in order to support PCIe x4. B key connectors only support PCIe x2, which not many manufacturers produce since it's much slower. Only the SATA SSDs seem to have the M.2 B key connector, which I'm not sure is compatible. Thanks!