Same problem here, Opera TV on BD Player HT_H5500w which is in the supported list of players, and Plex should be available, but isnt. This is the sole reason I buyed the player after scrutinizing the web to ensure that plex was available, as stated here :

http://www.operasoftware.com/press/releases/devices/2014-12-10

Can opera support please join in on this discussion?