From my line of work, what I sorely need is a cross-platform (macOS, iOS, Windows and … OK … perhaps Linux if it seems easy enough) literature reference manager app combining the best of citation managers (Bookends and ReadCube Papers) with the best of literature search engines (no-nonsense EZProxy direct tunneling + Google Scholar + …) with the best of annotation markup engines (PDFExpert) with the best / most innovative of annotation management tools (MarginNote and LiquidText) with the best search engine (DevonThink + GREP + complex query chains).
In any case, by the time I would consider the benefits of the first condition and the headaches to fulfill the question itself in the way that I’d really like to see it done, I’d realize that I would do better to pay someone to do it for me while I go skiing in the Alps.
So, I’d opt to pay handsomely to the developers of those other apps to make their apps talk directly to each other.
As a side benefit, I don’t really like the “everything and the kitchen sink” approach anyway.
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JJW