The passing track is already in place and I believe they are working on signalizing it right now. Also the plan is to signalize a good portion of the line, not just around the passing track. Its not as quick and easy as it sounds though.
Once they've finished that, hourly service will be no problem. They could technically run all-day service on the line without signals, but trains going into and out of the passing would take a huge delay every time they use it, not sure if they could maintain hourly service in that case. Plus there's an added level of safety with signals. People can screw up train orders much more easily than missing lights. Both are extremely rare occurrences, but you only need it to happen once to result in a devastating accident. It reminds me of a quote some terrorist bastard said one time - You have to get lucky all the time, I only have to get lucky once.