You know what just occured to me -- Slack is effectively 'inifinite scroll' too (no pagination), of quite a bitof content sometimes... and I don't think people complain much about this aspect of Slack. Wonder how they managed to get it right.
Because Slack is a chat system and you typically just care about the most recent messages (which are always displayed). I find scrolling back in Slack to actually be very irritating, when I have to do it. It's slow and the view jumps around whenever the next page loads in. (The UX on the search functionality is also fairly lacking.)
Yeah, people basically don't care at all about chat history. Chat is short-term memory; forgetting is a feature.
They add a nice ("109 comments since April 30th") link to click at the top of the chat window that does exactly what it says. Also there's a custom search box so ctrl+F isn't as broken.