It has been stated: New Post: Librem 14 Status Update: EVT2 Sample Is Almost There - #5 by Kyle_Rankin
That is true but it is my understanding that that is not the case in the Librem 14 i.e. the M.2 slots in the Librem 14 have both sets of pins connected and the chipset supports both interfaces (and within PCIe support, specifically supports NVMe).