This is an out of the box idea.
While readingm please forget technical difficulties.
Look at other software:
Firefox/chrome/mobile apps. They all auto update.
Could we not arrange that the drupal core (or a distribution) automagically updates itself?
This could more easily be done between major versions, it is too late for drupal 7 to do this, but drupal 8 could do this.
It could itself get the latest security patches(in core).
In my dream drupal, also major versions are automatically pushed (with webmaster approval). With chrome (or ubuntu) like behavior. It is offcourse required that contrib modules can be disabled on update because of api version(or other) problems, but thats the consequence of the new version.
This comes closer to Dries's continuous innovation than releasing new versions ever x time (I think).
This could also be the last drupal you ever need to install, because you will never need to reinstall a newer version. The magic will happen itself.
Most softwares have changed to auto update themselve. Is it too crazy to have drupal download latest core itself and replace the needed files?