Chat system is right at the top of the list of future updates! As for the poke feature, we actually do have a "nudge" button that appears after 24 hours of inactivity per game.
How 'bout a "search by name" (instead of username?) I don't seem to be able to start a game with a friend's name... (E.g. I am playing with Sean B. I lose the game and I want a rematch. I go to "one on one", then I choose "find by username" and enter Sean B. It returns a "could not find user" message.)
Good point! Right now it's not possible, but one of the first features we are going to add along with the chat feature is the rematch option. That will always let you start another game with the same user if either person would like to.