Firstly I'll say I know about the option to hide events from chans but what I'm suggesting is a twist on that.

It would be nice if that option could be toggled on/off and previous events would be shown. I personally like having joins/parts/quits hidden since most of the time it's just spam breaking up chat. But since I'm an op in some chans It's handy to look at those events when there is trouble.

Channel windows can't add or remove lines due to their design. This would need to be added first, and AFAIK it's fairly complex to do-- but if it were done, we would have the ability to use /iline or /rline in channel windows, and then this could be scripted. In other words, if the infrastructure was there, this would still be something that would be better off scripted anyway, since there are many possibilities for event types to hide.