Second of all, we will continue to support building Ionic apps with Angular. In fact, you shouldn't really notice any difference, we've just turned a number of the Ionic components into web components. It'll be fairly seamless but performance on load and code size should improve by a fair margin.
Long term? It's hard to argue against web components being a superior deployment option for both our components and your apps, so if developer preference shifts in that direction we might push stencil/web components as the default. Time will tell