Although lets be honest here, free apps could easily continue to be subsidised by Apple in any future model. We are talking about far less than a dollar per iPhone in terms of hosting/bandwidth costs for all the apps, so this really is something that Apple could easily just swallow.
Let's not forget that the availability, quality and abundance of apps, made by developers, is a key driver of success of the iPhone, and Apple makes plenty money from hardware sales. I won't lose sleep over the thought that they might have to pay for some hosting.
That's including AWS's insane profit margin, though. I have my cloud deployments with Hetzner, where extra traffic costs € 1.19 per TiB, so that 100 MiB app download would not be half cent, it would be 1/100th of a cent. (And that's before we consider that Hetzner gives 20 TiB per month free traffic with every VM.)
Now imagine your app is free. Yet you have to pay for all these downloads. There wouldn’t be any free apps anymore.