I'm not planning on supporting split panes (though I'm sure that feature will eventually be written), instead relying on multiplexers like tmux to fill that gap for the time being. I don't really know enough about tmux's control mode to understand how I might integrate it but I, personally, didn't like iTerm2's integration much so if I did interface with tmux at a lower level then it might look somewhat different to iTerm2.

That all said, at this point in time I'm not discounting any ideas.