I think the server I was on today was running a buggy version of an old plugin, but it was kind of fun. It allowed players to respawn in arena mode, which effectively turned all arena maps into king of the hill. I think this happened in old versions of the fast respawn plugins.
To make it even better, it'd do all of the following:
1. Unlock the CP after 30 seconds (this is a normal arena cvar).
2. Make it so the round doesn't end when all players are dead... only on capture.
3. Increase the capture time of the CP (not sure what it is now, but increase by about 10 seconds).
4. Force respawn after x seconds, where x is the number of players on the server (cap at 20).
5. [edit] Allow teams to be unbalanced by 1 player, allowing everyone to play. ;)
I know this doesn't fit why arena mode was created, but we have a lot of players that don't like sitting out after they die in arena. As a result we never get to play it. By making a "king of the hill" mod like above, it'd automatically make all arena maps work for us.