> I would love to see SQL grow a concise navigation/join syntax

Yeah, what you need is a specification of a name to use for the referenced table in implicit joins when you sepcify an FK, then if you reference the linked table, it performs the join (to bring in a different subthread, such an implicit join specification could be the mechanism of opting-in for index-free adjacency on that FK, too, so you'd combine syntactic support with the supporting query optimization.)

Maybe something like:

  REFERENCES <table> [(<key columns>)] AS <link-name>

So, your example would be be supported by (assuming all the FKs are to PKs so you don't need columns specified on the FKs):

  FOREIGN KEY department_id REFERENCES departments AS department

  FOREIGN KEY head_id REFERENCES employees AS head

  FOREIGN KEY assistant_id REFERENCES employees AS assistant

...on the relevant tables.