There are so many chat managing plugins out there, it would be nice if Vault could do as they did with economies and make it easy to hook into / message through these plugins such as CraftIRC 2/3, HeroChat 4/5 , ChannelChat

it does... see Chat.java - if you mean actually changing messages. No. that arena is way too messy there's no way to standardize it. just choose one. You'd like to support. I don't really see much benefit in creating a split on supporting messaging plugins directly. What methods would it use? What information would it push? what would an API for these do?

All of these plugins simply take commands and push out messages to people.. not sure what you'd want vault to do for an API that hooks these.