bool
VRCPlayerApi.Chatbox.IsTyping
string
VRCPlayerApi.Chatbox.Text
This opens up possibilities for chatting (with text) as a way to interact with the world, e.g. NPCs responding to certain keywords you are "speaking".
Or world specific custom placement of Chatboxes. Maybe someone wants to do a presentation and needs their Chatbox enlarged for a large audience. This will be equivalent to player audio setting a higher voice gain.
This allows chatting to be an actual game mechanic in VRChat.