I think this would be a great feature, because it's quite annoying if people keep adding you to grouped conversations. It goes like this. When someone invites you, you get a pop-up message with:
"<username> invited you to a grouped conversation. Here is a list of participants in this conversation.
<list with users and their e-mails>
Would you like to join this conversation?
[Yes] [No]"
It would also come in handy if there is a person in the conversation who you don't want to talk to.

That has been suggested several times before, and the result was that that wasn't possible. When someone invites you into a convo, the protocol of messenger doesn't say who invited you.