Naive discussion wish: If every post is required to be a reply to a specific post (twitter kind of achieves this) and also has a timestamp, then you should be able to set threaded or non threaded display as a preference. You could even click on a post ask for something like "show 3 levels above and below threaded for this post" if in flat mode and vice-versa for threaded. Forcing a reply target helps avoid the non-sequitur posting you get on flat discussions