I would never, ever ask anyone to read that much. Especially since, that far into the RP, you really don't need to know the vast majority of it anyway. Depending on what exactly has gone on, you usually only need basic plot points - as well as a quick run-down as to how all the characters got to where they are now as of you joining.

If a GM is going to allow people to join once an RP has gotten that far, they should be able to provide a basic summary. Don't think anyone can join unless they actually read every tiny (or not so tiny) post? Then there's no point in keeping it open to new people.