Yes, there should be a discreet button to use at will to invite commentors to a chat.
The current heuristic often fails to intervene until after it's:
- too late to prevent chatty comments from accumulating
- too late for there to be any further discussion needed
I find I simply ignore the popup most of the time, since by the time it shows up, I'm done. It comes too late to serve as a reminder to avoid back-and-forth commenting, and often it only shows up when nothing more needs to be said.
A discreet button would serve as both reminder to avoid discussion in comments and as call-to-action to the alternative. Not to mention, automating the option earlier would make it more frequently chosen earlier — currently it can be done manually, but that is a high-barrier multi-step option that is not often remembered let alone chosen, compared to the low barrier of "just squeeze in one more comment."