I think the big potential use cases already have projects - smart contracts, IoT, and fast secure digital money with zero or low transfer fees. There is huge room for growth in each of these, both with the existing projects and the newcomers. Another big use I think will be proof of provenance, stuff like WaltonChain.

As for whole new use cases for which there is no existing coin, I'm not sure. The world is waking up to crypto, and applying it to everything. As soon as a new use case becomes apparent, you can bet that someone will create a coin for it.