Wouldn’t it improve the security of the internal NK-storage to have a timeout-feature, which locks the disk after a certain time of inactivity - as we see it in many password-managers ?
The idea is valid, though firmware side it is hard to detect whether the disks are unused and the write-cache is flushed to the device. At the moment we could safely do PWS autolock as in Pro#43.
Nitrokey App side - it could ask user to confirm the device lock, though this will not cover cases where Storage device is left powered on in the USB slot.
Do you have any specific use case?