I feel like the discussion here has skipped a step, namely..

Originally Posted by Khaled
mIRC intentionally prevents another /list request from being sent if a listing is currently in progress. This was implemented very early on in mIRC's development, when users were being regularly disconnected from servers due to sending too many /list requests. This was due to servers having difficulty coping with the bandwidth needed to repeatedly send lists to users. So mIRC tried to decrease the strain on servers by preventing users (especially new users) from queuing multiple /list requests (often by mistake, especially if there was lag and issuing a /list did not result in an immediate reply from the server).

..is this restriction, which certainly was a good thing at the time, still relevant today?

Saturn, QuakeNet staff