It will be more of the same, but with an increase of BS threads. After the manga is finished, then people will be more active about the anime. Once the manga is finished there will also be people who are simply viewing the manga, either for the first time or revisiting it.
There wont be anymore threads that have to do with predictions and or reviews because the presence of suspense will be gone as the manga will be over. There will be an increase of fanboy threads, vs threads, most likely "what if" threads, and again threads by newcomers to the manga. I don't want to say there will be more trolls, but people will certainly be more bored than they are now and more will be tempted to troll or intentionally try to spark unnecessary threads.
You can expect less traffic as people wont be crowded the server every wednesday, and the clogging up the thread feed with chapter reactions, so if you have a decent thread it might actually get viewed. Whatever the case may be, the site will still exist for people to enjoy the chapters and the anime, after all that is this sites sole purpose.