INSERT ... ON DUPLICATE KEY UPDATE is useful when man wants to update table with foreign keys from CSV file. REPLACE won't work in this case as it first deletes the row and then reinserts it, what breaks constraints.
Was this feature request worked on?
I don't think anybody is working on this.
Implemented with https://github.com/phpmyadmin/phpmyadmin/commit/6f9367b1652e6b5cee652ab4729bb0253ac74b95