Would anyone anticipate problems if the SD Card hosted the PiFi while the attached NVMe drive hosted a normal desktop environment? With this setup I would just change the Boot Order to access a standard Desktop Environment or the PiFi Router mode as needed.
While I haven’t yet tested it myself yet - I see no reason why that wouldn’t work.
It should be fine to change boot order and boot from USB / NVMe / SD (PiFi) by changing boot order. If you do give it a try successfully please reply on this post just to confirm
I do have a NVMe Drive so I can also test this soon but I’m pretty sure it’ll work fine