Storage capacity is not much of an issue so a raw uncompressed format such as WAV may be preferred.
This would not be suitable for audio recording, but the file format could work equally well for sensor data which from a Nano point of view is just voltage variations over time as is raw audio. It might have applications for recording temperature variations, battery charge/discharge voltage and infrequent signals such as relay control signals. A programmer might read the data and process it on a PC for further analysis, but any simple audio editor could also be used to just load and display the waveform on a PC.
With the latest firmware updates we’re close to using every single byte of RAM on the Nano and so new features will be hard if at all possible to add. Considering that this may be the last feature we can add to the V3 firmware, is this the best candidate?