thanks to @Quiddity for suggesting this improvement

. However it's nicely responsive and works well (at least) down to 720px wide windows

I think this is a false impression related to the disappearance of the language button from the sticky header.

Consider the following

• We'll soon be expanding the sticky header to include 2 additional edit icons (VE and edit source).
• We will be adding margins in T314323 to the right of icons
• Long titles

With the above changes, we're struggling to fit the 1000px breakpoint so this will not easily scale to 720px without some additional code to adapt:

In T315611#8167156, @Jdlrobson wrote:

Consider the following

• We'll soon be expanding the sticky header to include 2 additional edit icons (VE and edit source).
• We will be adding margins in T314323 to the right of icons
• Long titles

Here is a screen recording including two additional icon buttons, the 8px of space between the icon buttons, and a long title:

With the above changes, we're struggling to fit the 1000px breakpoint so this will not easily scale to 720px without some additional code to adapt:

I agree that we could make some changes to fix it up even more, for example:

• drop the 82 languages and just use the icon
• remove some of the other icon buttons
• remove the page title

but even without making the changes I think it's an improvement to retain the sticky header until 720px

In T315611#8168578, @ovasileva wrote:

@alexhollender_WMF - this one doesn't seem like a blocker. What do you think?

agreed, not a blocker

I'm not doubting it's an improvement, just a lot of added technical complexity and additional work for a small group of logged in users who resize the browser (note tablet users already get the sticky header).

I forget what I said that led to the mention above (in August), but currently I really value having the sticky header at all window-sizes (including whilst logged-out).
I've got a lot of subtle customizations in my userscript; it's not perfect as I'm not a professional CSS-wrangler, but I really like it, especially the full-size search box for easy-clicking. Here's a recording of (part of) what they result in, for the sticky header: