A simple idea: ability to recall the last twenty or so messages on cabal/clan channels (this wouldn't be very stressful for the server, since there's a limited amount of those) and, if possible, for tells.
For tells, logoffs might as well clear those, if necessary. For cabals/clans, an elder/leader could possibly enable/disable this function if speaking behind people's backs is the thing for that particular organization (and they're too lazy to spam out such from the channel, or to use tells/says).
You want to be able to see the last 20 cabal says, even those before you have been logged?
Sure, why not. Most any application of the idea would be nice, though.
Its fundamental goal would be to enhance interactive RP in a small way.
Yeah, but I wouldn't want anyone to see me
f0xx cabaltalks: "asdasdsad"
f0xx cabaltalks: "Alright, the standard is at its place."

You can easily do this in zMUD using the trigger system. Just set up three triggers like this:
(%w) tells the group *
You tell (%w) *
(%w) tells you *
and have them execute:
#CW white
#CAP Tells
Creates your own tell/grouptell log and also highlights them so you never miss them in spam in the main window.
I re-read through these a lot and would love to see it integrated into the MUD itself.