A ''search all'' function was suggested before. I'd link you to the thread but obviously it's all been nuked.
Soda addressed it as something that wouldn't happen. I can't remember the details.. something to do with the fact everyone searching for such an amass of people at once breaking loading/flooding too much at once..or something like that. It was all rather technical.
And inevitably while I like the idea, searching all would have to be done in order to view online users. Rather than one singularly like now.