I enabled by default now. It was disabled because we've been turning features that could possibly encourage turning threads into chatting places among repliers off but it seems wanted by enough people, and futaba too has it...
If you are reading this, you should still click [settings] at top right read through it. What we have by default is merely what I think is acceptable for the majority of users who will never bother clicking the buttan, you may liek it better with some changes