I think the part of the problem with diaries like this is psychological - the format of the site encourages substantial, but not too long, diares. I started reading it with no idea how long it would be, found it very interesting, but didn't have time to study it carefully once I realized that it looked as though it would never end. A warning that it is long might help (but I might just skip the warning...). Another possibility might be to split the diaries inyo several of moderate length, and post them with a short interval between them. That might even encourage people to discuss the content of the diary, rather than its form.