Maybe this would be kinda odd, but what if they combined the turnstile system with proof of payment. Stations would not necessarily need agents to monitor the turnstiles especially with the new automated machines if people swiped their passes to gain access to the platform, but would still be subject to show proof of payment if asked by transit police. Not even all (more heavily used) stations in bigger cities have an agent present all the time the station is open. This would at the very least allow the "honest" passengers, such as those who were interviewed in/commented on the article in my last post, to pay - even if the on board collector is down.
And yes, yesterday I did notice clear signage at all the stations explaining POP. It did however confuse one passenger, who I assume was from out of town, at the airport because as I said there were signs on the booth, turnstile, and new ticketing machine which said to pay on the train, but also another just beyond that area which said that in order to enter "that area" you must have already paid. I helped him and told him that the system is "transitioning" and to pay on board.