Enhancement request - fragments in _includes/*.html for page header and footer

[peterjc]

Apologies if this is the wrong place to file a cross-theme issue, but it seemed more sensible than filling multiple issues or picking a single theme at random.

A few years ago all the themes got _includes/head-custom.html added which in turn includes _includes/head-custom-google-analytics.html to aid customizing Google Analytics. This was mostly the work of @parkr e.g.

pages-themes/cayman#133

pages-themes/primer#61

pages-themes/hacker#69
pages-themes/hacker#79

pages-themes/modernist#16

pages-themes/slate#66

That makes various styling customization easier.

In a similar approach, I would like to see _includes/page-header.html and _includes/page-footer.html (or similar filenames as long as this is consistent between the themes) in all the themes to make it easy to adjust the contents of the top banner (e.g. adding a logo) and footer (e.g. expanding acknowledgments, adding social media icons).

Is this something the maintainers might accept in principle? Is it worth me making a test-case PR for my preferred theme? Thank you!