I wonder if they are going to leave the old forums up. I find them useful sometimes when watching films and wondering if I've missed something from the plot or want to learn what others made of ambiguous endings.
Trolls certainly can wreck a board for a film, though, to the point where the film is hardly discussed. Black Death and Young Messiah mostly have idiotic, pointless fights between atheists and Christians on the majority of the threads.
I suspect IMDb wants to move to discussion to Face Book to be able to sell info to marketers rather than because they care about users' experiences, but that's just my cynical opinion. And then of course they will be able to control which films are discussed and which are ignored.