They seem to be switching business models again, or may be that was in the original plan.
They started by giving the app for free to gain market share and make the publishers install the server part. Then they started charging one time fee and providing future updates for free.
The problem is that when you start approaching the saturation of customers willing to pay for such an app the revenue drops dramatically. So they're trying to generate money by ads and hitting again the customers who have already proven willing to pay. So they'll be like traditional software companies charging for each upgrade (unless they can get paid through ads, but that seems very unlikely given how poorly they did in their past attempts).

At the end of the day the basic economics is still here - they want to be paid for the work and once you hit the limit of how many times you can sell the exact same thing you have to make something new and convince people to buy it.
A competitor will have to deal with the exact same problem, and it's not clear if being upfront about having to charge repeatedly will help them. Or they could repeat the same thing tapatalk did, but it'll be a shame if it works.