Yeah...if this gets implemented, please please please make it a toggle whether or not other people see you typing. I like having the freedom to either start typing something and then either change my mind about sending it or to change it around a lot because it's too mean/not mean enough/doesn't have enough maware and I would really rather the other person not know that I spent so much time typing something that they never saw.
Strangely enough, I don't have that feature disabled on skype, but...well...a lot of people I talk to/who talk to me on osu! are people I would never add on skype. Communication channels are much more open in osu! (you can message most people even if they haven't friended you, you can't prevent anyone else from seeing you online or from spectating you if you're playing, you can't have osu! open in any way that will allow you to use online functionality without osu! notifying you whenever anyone sends you a PM, anyone else can see when you haven't tabbed to osu! in the past 5(?) minutes, etc), which leads to more interaction with people one wouldn't normally choose to interact with and having this extra bit of privacy forcibly taken away would make me a sad frog.