In /advanced-options/svg-sprites/ /sprites/, you are already providing 3 SVG files with all free icons collected inside them, but there is no ready-made CSS file that references them like the default webfont glyphs.

.fas-foo 
{
  background-image: url(fa-regular.svg#foo);
}
.fas-foo-before::before, 
.fas-foo-after::after
{
  content: url(fa-regular.svg#foo);
}

Related: #3203, #14280, #10352

Is this in relation to an existing part of Font Awesome or something new?

This offers a readily usable index of already available files.

What is 1 thing that we can do when building this feature that will guarantee that it is awesome?

Authors who chose this option would not have to use meaningless Unicode PUA characters that also will never be displayed with an unintentional font.

Why would other Font Awesome users care about this?

Since authors are moving away from font files for decorative symbols, an SVG-and-CSS solution that uses basically the same markup authors are used to, should look attractive to them.

Feature request checklist

• This is a single feature
• The title starts with "Feature request: " and is followed by a clear feature name
• I have searched for existing issues and to the best of my knowledge this is not a duplicate