User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-126761-20150520121535

Regarding concerns about article layouts being negatively affected by this change - due to the nature of this change, if you're seeing issues with articles now, that's almost certainly because they already had issues for a significant number of your visitors. This is a fairly major reason why this change needed to be made.

With yesterday's update, many of your visitors will have noticed almost no difference - because they aren't on large screens - they're on mid-size laptops, or tablets. What you're seeing now is what a lot of your visitors already had to contend with, because many articles were designed against the largest of screens, without realising the effects on smaller screens.

We don't blame you guys for not realising this - it's a pretty difficult thing to test. We don't expect you to test every article you write on multiple devices, nor spend minutes checking each edit on different preview sizes. That's not reasonable.

For the long-term, we strongly feel it is better to have a more consistent article layout between devices - it means you can create an article and not have to worry about whether it'll look broken for some.

By no means do we think it is a perfect solution - those don't really exist - but we do think it makes the most sense for the future.