I got it to compile like this:

#[derive(Debug, MessageResponse, Serialize)]
pub struct SnakeBody(Vec<Pos2d>);

impl Handler<ExecuteTick> for Snake {
    type Result = SnakeBody;

    fn handle(&mut self, _msg: ExecuteTick, ctx: &mut Context<Self>) -> Self::Result {
        println!("Snake::ExecuteTick");

        let (sender, receiver) = channel::<PlayerInput>(100);
        let mut inputs: Vec<PlayerInput> = vec![];
        for client in &self.subscribers {
             client
                .send(GetCurrentUserAction)
                .into_actor(self)
                .then(|res, _snake, ctx| {
                    if let Some(input) = res.expect("unable to collect current user input") {
                        //inputs.push(input);
                        sender.do_send(input);
                    }

                    fut::ready(())
                })
                .wait(ctx);
        }

        //MessageResult(
        SnakeBody(self.body.clone())
        //)
    }
}

Now I would like to collect the results from the subscribers, but I get either moved out error or the channel can not send the results back.
Does anyone have any idea?