If a topic has hundreds of pages of answers and it does not matter to the reader what was said in the beginning, it does not represent quality content. In quality discussions every contribution counts.
Discourse already provides the function of beginning the reading experience where you ended it.
Why would it not be necessary to read all these posts in-between? What makes latest posts more valuable?
Edit: If you don’t care about the old posts, you would not keep scrolling to read them. Do you only want to see the latest updates like, for example, I would want to read in a “news” feed aimed at entertaining me?