If it were a dielectric panel it would be evident on all 717s unless it were suddenly retrofitted on this one aircraft only.
If it's indeed a VOR receiver it would have been there on delivery, and on all 717s.
There is no equivalent on the other side of the aircraft View Large View Medium
Photo © Daniel Wojdylo
but some peeling paint IS
visible there (that photo was taken about a month earlier).
Theoretically the aircraft could of course have been retrofitted with some expermintal equipment but I doubt they'd do such a sloppy job of painting the fairing