I've seen recently the IIIF API task on Phabricator (https://phabricator.wikimedia.org/T247857).
Do you have more details about what is intended behind this general task?
Is it related to the proposal from the 2019 community wishlist on supporting the IIIF Presentation API in Wikicommons? https://meta.wikimedia.org/wiki/Community_Wishlist_Survey_2019/Multimedia_and_Commons/Support_for_IIIF_Presentation_API_in_WikiCommons. If that is the case, do you have an idea of the timeframe for implementing this?