"Comments are not for extended discussion", the Stack Exchange system always tells us if it detects two people getting into a 2-way discussion in the comments of a question or answer.
However when inviting a user to a chat room as below:
there is currently no feature available to transfer (or at least copy) the comments in the existing discussion into the new chat room, unless creating a brand new chat room, which I think is extremely inelegant.
My first feature-request, which you can see in the above link, was unsuccessful (in my opinion due to just one user who unfairly attacked the idea). However, I think the above screenshot is a perfect example of why the entire SE company (not just me!) would actually like for there to be such a feature. Therefore I propose that we keep in this Meta discussion, a record of such examples as this one, in the spirit of accumulating enough data to make the feature-request successful.