This is a feature request just like the one I just opened for vimtex. It too is based on an old thread from a year ago about how doing so might be feasible.
What I would like is to be able to enter a single command (in the case of wiki.vim, simply <CR>) in order to open the citekey under the cursor in BibDesk (on MacOS). Unlike in vimtex, I don't think wiki.vim "knows" which .bib file to use, so perhaps it would make most sense for it to simply be a reference to whatever .bib file is open in BibDesk at the time. I think this might be what open x-bdsk://citekey (see description here) does by default anyway.