"Bob is typing..."
"Bob and Phil are typing..."
"Bob, Phil and 3 others are typing..."
"Bob and Phil are typing..."
"Bob, Phil and 3 others are typing..."
Though I suppose you could visualize it in the nickname somehow. But I hate the current retrieve trend of "and 3 others". It didn't really tell you anything if one of the other participants is someone you want to know about. Because you still don't know if any of them is typing or not.
If it's important, show it for everyone. Otherwise don't bother showing it at all. But showing it for some randomly picked users makes no sense.
Then again, in practice I found that if more than two or three people are typing at a given moment, it's probably a conversation that's lively enough already, and I'd usually just wait to see what the participants end up writing regardless of who it is. So the value of such a notification is about the same as if the all the typing users were named in it explicitly. :)
Phil: I'm just walking down a fine wee snicket.
Bob: What's the frequency Kenneth?
Phil: ■■■■■■■
Bob: ■■■
3 others typing...