I know it's just an example, but it's really straightforward: you create a component which accepts a boolean prop and, based on that, either outputs the default

I know it's just an example, but it's really straightforward: you create a component which accepts a boolean prop and, based on that, either outputs the default slot directly or a wrapper containing the default slot via a simple v-if. If you wanted to get fancy, you could also accept a tag prop and v-bind all other $attrs on the container to make that a general purpose component.