I'm pretty sure a diamond lounge will be added.
I saw a PDF file some time ago where it said "Diamond Club" to be added to most of the RCI ships (not all though, but maybe those where it was not mentioned already has it).
Mariner is already revitalized and the Diamond lounge is in Viking Crown, in the area for the former sports bar (19th hole) on starboard side.
NAVIGATOR OF THE SEAS - 7/6/14
NAVIGATOR OF THE SEAS - 9/14/14
NAVIGATOR OF THE SEAS - 9/21/14
OASIS OF THE SEAS - 10/14/14
NAVIGATOR OF THE SEAS - 11/4/15
NAVIGATOR OF THE SEAS - 1/11/15