I wonder, if a whole post that has only off topic comments, could be marked by the thread op user as off topic, and therefore be shrank to a single line, and have an off topic tag on it, and not count on the posts per page limit, so we always have 15 visible topic related posts per page.
They are visually obtrusive and put away the flow of the topic, so you dont know if the next page of comments will have something related to the topic and may give up reading it; I mean ppl can talk offtopically as some matters are important, but the one browsing the topic may not be interested on that other subject at all.
So, who wants to read the off topic comments just click to unshrink each one or them all.
Also, users that abuse putting off topic tag on posts (that are not completely off topic) could loose that right.
And finally, other users could vote to the topic be marked as off topic, requiring at least 3 votes.
PS.: (off-topic) I was trying to search for an off topic thread subject, but the second time I tried, I also clicked on an arrow there “>” and after that the control bugged out and when I clicked the up-right icon again to expand it, only a close button would appear and I could search anymore even after re-login 
TestCase: if ppl talk about the PS above exclusively, that post could be marked as offtopic and shrinked :D, otherwise if we get a whole page talking about the PS, this topic is no more xD
EDIT: we can do it like in:
Offtopic about some stuff
this is some stuff that wont bother you if you dont open this 
just click the gear and “hide details”