In future miners will be rewarded almost exclusively with transaction fees.
The idea is that bitcoin is widely used with millions of transactions on each block, so those fees will be enough.
For that to happen, there would have to be a solution to the scalability issue for the network to accommodate that much transactions and keep it running at a productive pace.
It would be an audacious attempt, to make a prediction for over a hundred years from now. And would simply be just choosing figures.