I'm still missing how to reliably detect if a device is a "wired" or a "wireless" one. I suspect that checking the existence of /phy80211 would be enough, but I can't really tell, and seems like I'm not able to find an exhaustive sysfs reference manual.
Sadly there is no exhaustive manual, but many attributes found in sysfs are documented under Documentation/ABI/. In this case you need the DEVTYPE name from the net device's uevent, which may be e.g. 'wlan' or 'wwan' (and is absent for wired Ethernet devices). I don't know why this isn't also exposed as an attribute in its own right.