After a long time of "testing", the button "old version" has finally disappeared from the new google analytics interface.
If you have been using the old version up to now, and for some reason you would like to revert to the old one, here is how:
Navigate to google analytics on a browser.
Create a cookie (or edit an existing) on your browser with the following data:
Expires Wed, 18 Apr 2017 12:25:02 GMT
Open a new tab and navigate to https://www.google.com/analytics/settings/home