Feature request: add a date-stamped, permanent, append-only comment field to each device.
This would allow for a historic log of user-supplied information associated with each physical device.
Tracking battery replacement frequency (a metric for devices that are too chatty on the network, devices with marginal connectivity, efficiency of devices, quality of battery brands)
Noting performance/feature changes depending on firmware. For example, I've got 15+ water sensors. I would update firmware on a small number of units and note any differences in behavior between firmware versions before doing a mass update.
Note particular characteristics of devices. For example, that one brand of motion detector responds more quickly than another, or that one brand of device works better when close to a repeater than another.