For the old (native) Papers3 version, I’ve written a “Papers to DEVONthink” script that exports individual note files for all notes & highlight annotations (of all publications selected in your Papers 3 library) to DEVONthink. It also indexes the primary PDF in DT and can transfer many more properties. These exported annotation notes can form a good basis to work with them in DT.
That said, AFAIK the new Readcube Papers version doesn’t have the scripting API anymore but maybe there are/will be server-side hooks? ATM, only the Readcube Enterprise edition lists “API Access” as one of its features.