@naachan and @Hel: I’ve added a pagination option to our to-do list in this sub, but it’s unlikely that this will happen as this is the official Discourse word on the subject:
https://meta.discourse.org/t/being-a-heretic-aka-going-back-to-pagination/52070/2
That thread also mentions that you can disable javascript and Discourse will default to a pagination mode. I just tested it and while a lot of the layout of the site is destroyed, it does work.
Something that could fix both of these problems is, like @Hel mentioned, a way for each user to control the amount of content being preloaded. A problem with making that content based on posts is that a single post can contain a huge amount of text or imagery. Maybe a better way to do this is to control the amount of text and bbcode being loaded on a per-character basis? I’ll add this to the list of things to approach Discourse with. As with all the other things on that list, if this doesn’t work I’ll see how much a plugin to add this functionality would cost.