When somebody replies to an older message in chat, you have to click the "in reply to" arrow and jump to the message to get the context. That makes you leave the current position in the transcript, and old content possibly even needs to be loaded first. That's often a bit disrupting, especially when you're reading through the transcript.
Discourse has a nice "inline quoting" feature. When you reply to a post, you see a "in reply to" button:
When you click it, the original message is opened inline:
Would something like that make sense for chat? It would be much more minimalistic of course, just fading in the original message above the reply button. Here's a (sloppy) sketch what it could look like: