Alot of these ideas are really good. But in all honesty, what would make the biggest difference, would be /assist "player" This was a staple in FFXI. Sometimes you don't have time to mark a mob. Specially in the middle of a fight with adds because of a bad pull or whatever. One person called all the shots and all the rest of the party had to do was hit there assist macro.

I'm not against markers (though sometimes on larger mobs, you can't always see them if you are up close and fighting) I use them. But a player assist command would make things ALOT easier