Practically speaking it's done a lot. Even outside of web development. For example Gradle (a java build system) runs a daemon that hosts a bunch of tasks that

Practically speaking it's done a lot. Even outside of web development. For example Gradle (a java build system) runs a daemon that hosts a bunch of tasks that run and die. Docker does it with images. The browser does it with tabs. Php achieves it with the help of server components. That is fine, but I wouldn't advertise it as a feature.