In reply to Joseph.

We aim to be backwards compatible, so the Site Icon module will remain in Jetpack for a few more WordPress releases.

Jetpack is usually compatible with the current WordPress version, and the 2 versions that came before it. So you can expect the Site Icon module to remain in Jetpack for another 2 WordPress releases. Then we'll consider that to use Jetpack on your site, you must run at least WordPress 4.3, which includes Site Icon.

This ensures that the option doesn't suddenly disappear just because you're running an older version of WordPress.