Dmitry Gutov <dgutov@yandex.ru> writes:

> It would be nice to have a set of general purpose icons available in
> ELPA, or ever in the core. For this and other purposes.

Yup.  Have a look at the attached quick mock-up of how things could look
if we would use Material icons for the tool-bar as an example.

> For now I'm using vscode's ones (under CC BY 4.0), but I'm guessing it
> won't be good for Emacs's image to migrate to that wholesale.

True.  all-the-icons.el has some links to other freely licensed sets.
Could one of them be a suitable replacement?