It would be nice to have $chan work in an ON NICK. What if you wanted to limit the ON NICK commands to 1 channel for a script?

It makes no sence why $chan does not already work in ON NICK.

ON NICK won't give $chan because it's not a channel-related event. Could it check common channels between you and $nick? Yes, but there is $comchan already.

/help $comchan