There's a lot of comments on the google doc https://docs.google.com/document/d/1SX204J8zdbCiJu9ttuz-i_Al3emY-3-mDk9EHvAkqrg/edit# where this has been copied from. None of them seem resolved, so they should be carried over to here
Topic on Talk:Core Platform Team/Initiative/Core REST API in MediaWiki/Design principles
I just blanked the document. I'll let Daniel and Tim go back through this wiki page and see if they want to bring back up any of the unresolved topics from that discussion.