Level 1 support already received a TAG review (https://github.com/w3ctag/design-reviews/issues/170, https://github.com/w3ctag/design-reviews/issues/179) and Level 2 was discussed in the TAG review for Share Target (https://github.com/w3ctag/design-reviews/issues/221).
Web Share is an API set for sharing data (text, URLs, files) from a web app (to which the data is already available) to an app of the user's choosing. This has already been implemented/shipped in Chromium for Android and has been implemented/shipped in Edge for Windows. The Windows and Chrome OS implementation of these APIs will be shipped in Chromium 89.
This implementation is intended to add macOS implementation for these APIs in Chromium and will include support for both Level 1 & 2.
A website might like their users to be able to share their pictures and other files through social media, email, chat, etc. Since it will be soon shipped to more platforms like ChromeOS & Windows, this implementation will extend the support to include macOS to better allow websites to take advantage of this functionality .
Interoperability and Compatibility
Edge: Shipped Level 1 and 2 on Windows.
Web / Framework developers: The ability to share images and files has been a consistent request.
See also the Intent to Implement: Web Share API (Windows & Chrome OS) discussion: https://groups.google.com/a/chromium.org/g/blink-dev/c/PZkIB8wBTwQ/m/qfX1At8UAgAJ
See also the Intent to Implement: Web Share API (Android) discussion: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/1BOhy5av8MQ/OPPt76oZCQAJ
See also the Intent to Implement: Web Share Level 2 (Android) discussion: https://groups.google.com/a/chromium.org/forum/#%21msg/blink-dev/AiKgWvv3cq0/xAsjfSfMDQAJ