It's been a while since we did sth for the 404 page (MAGNOLIA-5754, for Magnolia 5.2.5 release).

/webapps/magnolia<Author|Public>/docroot/404.html

(https://git.magnolia-cms.com/projects/PLATFORM/repos/ce/browse/magnolia-empty-webapp/src/main/webapp/docroot/404.html)

The browser technology has evolved since 2014, and so I think we should also update this 404 page, including the message. 

My first intention was just to provide an updated text part of the page, but then I realized, the design of 404 pages today is a more complex issue, involving also marketing aspects.

See for example the reasons stated on this page: "11 Brilliant 404 Pages To Turn Lost Visitors Into Loyal Customers".

IMHO the updated default 404 page should be - design-wise - rather neutral and should work:

• For both pre-resurface and post-resurface mgnl designs, 
• Universally not only for magnolia-aware ppl, who don't mind seeing the Magnolia logo, but also for the end mgnl customers who could use our stock design of the 404 page in their projects instantly, before they find the time and resources to redesign the page in line with their corporate web styles.