BTW - I'm pretty sure that you can paginate comments and that there are Infinite Scroll plugins that will also load them progressively as you suggest. I just don't know them.
If you are getting a lot of intelligent comments and show them on the page, I think your page gets "stronger" over time - eventually you have every imaginable variation of your target phrases in the comments and sometimes, if you're getting really good comments, you can go back and update the article, moving the best info from the comments into the main article, which also strengthens it and is a nice "Thank you" to your users, who are usually flattered and more engaged.
And topic that generates 200+ is out of the ordinary. IMHO
Yes, they are. But when we land a topic like that, we don't want to let it go. In a thread that is getting a lot of comments, I am extra attentive to making sure commenters get a response and to just generally keep those active, because I think comments are the best measure of engagement on a blog. If you have a lot of pageviews and a high bounce rate, you might be doing well in search, but fialing your reader. If you have a lot of pageviews, a high bounce rate and a lot of intelligent comments, then you can guess the bounce rate is because you're actually meeting their needs and after that, they're done.
You still might want to do something about the bounce rate, but what you do in each case is going to be different.