Adám
The site selector is only visible in the main site listing view, but not on post pages or during editing. But there's usually plenty of space in the top bar, so I see no reason to omit it.
Please make it universal.
Top Answer
James Douglas
We have recently revisited the site switcher, and it is now on all pages and looks like this:

~~However we will also be rolling out icons for each community, like the C++ logo in the image above, which will eventually replace the colour blobs in the dropdown.~~
**Update:**
We now use community images in the dropdown:

Answer #2
Jack Douglas
Now implemented; see [@James's answer](/meta?q=645#a842)
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Thanks, we will be revisiting the navigation in the header shortly and will consider making it (or its replacement) universal