Picking up the discussion from #2583 (comment), I think it would make sense to distinguish between shell commands that helps to request or configure device or network properties and commands that are mostly meant as helpers during development or debugging. Examples for the first type of commands are ifconfig (to request network interface properties), chan (to set a radio channel) or rtc (to query the datetime) from an RTC. Examples for the last type are the discussed ncache (that manipulates IPv6 neighbor cache) and txtsend (to send link layer packets).