% channel names
 

In addition to # channels, I suggest having % channels.

A % channel would not be listed in the channel list and thus, only those who know the channel name can join, thus allowing privateish channels.

If you join the channel, it appears in the channel list locally to show users but leaving the channel will cause it to disappear again.

Maybe have player created and UC Server channels a %channel and the Gold/Classic/Hosted channels be #channel?

It would be better to implement channel modes to keep it resembling IRC more closely (especially if Stefan decides to re-allow outside access). If that was done, you could just set the +s (secret) mode to do precisely what you want.