A separate in-game tab for notes.

[zen330]

Should be an easy add, some reasons I like this idea are that it would avoid accidentally sending your notes (comments "to self") to your opponent in 1v1 games, and because it would be nice to have notes and ideas about the other team - or even one's own teammates that you might not want to share more publicly if they might risk conflict - to have all in one place.

Also for things you might want to remind yourself of for one move or in general and not have them getting lost in a potential sea of chatter.

[Apatheist]

I've already suggested pinning "notes to self" at the top of the chat. A separate tab for notes to self would work equally well I suppose.

[zen330]

I think the separate tab would work even better, as one might have many notes and might not want them taking up a lot of space in their chat box (and there would be less risk of sending your notes to others this way as well)