You summed it up perfectly, some senior Jio executives openly said that there is huge potential in mining data coming from high speed internet and its usage.
Another thing is that nothing comes for free. When 2G came, we were given the same unlimited data initially, which got us hooked on to internet. The same thing is happening with Jio 4G.
People whose usage was 2 GB per month will get addicted to using 10+GB. And the when the free period ends, they will be enticed to shell money to get more data. Also faster the speed of the internet, more data you are prone to use.
Also as all the calls are over data, so even calling someone will cost you money as it will be eating up your data.