If you had a way to somehow save the chat entries that happened at a particular cursor location, you have a way to capture the exact line of thinking / rationalization that went behind it. This would go way beyond arbitrary line comments while keeping your code clean. It follows that the more controversial / complicated segments of code will have more chat exchange between the developers. If a new developer were to be brought in to modify the code, it brings a very human element towards understanding what exactly the code does and why it was written that way.

I remember being brought into a 100K+ codebase as an intern and simply being overwhelmed at the prospect of trying to learn the structure and why it was written the way it was written. If the codebase also came with chat logs, it would've been an invaluable asset for me to pore over.

If I were you guys, I would make this into a full service that provides the automatic coding narrative. For any company that starts using this system, the value of such information will skyrocket over time.

I voted for OpenSource, but only because I think this is the kind of tool that can thrive in an OSS environment. I wouldn't let that stop you from setting up a service as well.