This post is the first in a series about getting Drupal to run as a persistent server, responding to requests without bootstrapping each and every time.
This is how many other application frameworks and languages run: nodejs, Rails etc.
In those systems you start some instances of your application and then they do whatever bootstrapping they need to do and then they enter an endless loop waiting for requests.
I recently upgraded our internally hosted Redmine server to run on Ruby 2.3 and during that upgrade took a look at our NewRelic monitoring for the application. Some of the page requests had an average response time of 8ms. These were page requests for logged in users. That would be amazing performance for a Drupal page.