In an interesting tweet from @BBM we see what they call [R]BOMBED, seeing when a group chat has read your message, as of right now the Read green icon only shows up on individual chats.
This has been a much requested feature as currently Facebook and Google Hangouts offer this feature, adding it to BBM would make it that much more exciting. Not sure how or when it will be integrated onto BBM but by the looks of it, it’s coming.