'Sticking with the unloved browsers after that date will result in what Justin Chung, director of product management at GitHub, delicately referred to as a "degraded experience".'
When he invented the world wide web a mere 30 years back, Tim Berners-Lee mandated the concept of client agnosticism, so that web content would be accessible regardless of the client being used.
By the end of that decade, as presentation on the web became fancier, the principle of graceful degradation was introduced, allowing the important (informative) content to be viewed even if the fancy presentation was beyond the capabilities of the client.
Now, you can't make use of many sites at all with scripting and style sheets turned off, as they're typically an unordered heap of content snippets shuffled and laid out by the scripts and styles, so with those turned off they're unreadable.
Haven't we made progress!