That's a really neat idea. Wouldn't be easy to implement as it stands, but it is definitely going on my list of features to explore. I have similar ideas in the works that will make the chat page more powerful and helpful to you as an admin.
Shouldn't be... Should be able to tokenize and parse the incoming chat stream. Since it should be in a specific format.
I know on FPSplayers.com's web console (not sure if this is how it returns via query) it is displayed: [CHAT] "user_name":"Body"
so just get the 2 values in quotes and if the body == flag -> add user_name to list.
I started working on an Rcon tool myself, written in Go (golang.org), but its nowhere near as cool as what you got going on here. Nice work. Looks like you have some good ideas.
Is that because there is no rcon tool for linux? Hit me up on twitter @utilitron, I'd be interested in helping out. I have been messing around with one in Java, one in c++, and one in php. I don't have a lot of experience with TCP sockets, but I have been programming a long time.