A good portion of org-mode's benefits come from the way it is integrated into various Emacs features, up to and including the fact that Emacs is completely repr

A good portion of org-mode's benefits come from the way it is integrated into various Emacs features, up to and including the fact that Emacs is completely reprogrammable. You can certainly replicate some aspects of that outside Emacs (and obviously people have done so), but in order to fully replicate that elsewhere, you'd more or less need to reimplement Emacs, or something on a similar scale. I think you also have the problem that Emacs' org-mode is effectively the de facto standard with no formal spec, and so every other implementation implements its own preferred subset of that "standard" based on what the author(s) found important. (Edit: I could be wrong about more recent non-emacs org-mode implementations. I haven't done a thorough survey recently.)