Not sure how accurate it is, BUT if you look at the deck plans for Mariner on cruisemapper.com, it tells what is going to be added during the dry dock in 2018. Here are the details:
Deck 14: the multipurpose rooms will be replaced with the Izumi
the Roller Skating Track and the Maariner Dunes golf course will be replaced by a FlowRider (surf simulator) and The Perfect Storm complex (Cyclone and Typhoon water-slides).
The waterslides complex is named “The Perfect Storm”. It is complimentary (cruise fare inclusive) and includes the RCI’s newest super-fun attraction “Tidal Wave” (aka Boomerango) plus 2 racer slides (“Cyclone” and “Typhoon”). Both spiraling slides are positioned portside and go around the Flowrider. Starboard is positioned the “Tidal Wave” (raft slide). It provides Mariner cruise ship passengers with the unique opportunity to ride in rafts plummeting down a very steep drop. Then the rafts shot up a nearly vertical wall into the air for experiencing the sensation of weightlessness and free fall. Then follows a swift return below. The slides builder WhiteWater. The company specializes in designing and manufacturing of water park products and family-fun attractions for major clients around the world. The company also owns the FlowRider patent (acquired from WaveLoc).
The aft-located FlowRider is the Royal Caribbean’s signature surf simulator. Pumps project high-speed water (20-30 mph / 30-50 kph) across a small area creating sheet waves (stationary waves) to simulate ocean surfing. FlowRiders were first created as land-based facilities and were implemented by Royal Caribbean for guests to enjoy traditional surfing and skimboarding on cruise ships. The Royal Caribbean FlowRider is a complimentary (cruise fare inclusive) facility and reservations are not required. Equipment (bodyboards, flowboards) is provided. Private surfing lessons are available for booking at additional cost per person. Groups are 6 to 8 guests. The FlowRider’s restrictions include min height (52″/132 cm to use bodyboard, 58″/147 cm to use flowboard). Not allowed are footwear, goggles, go-pro cams. Guests can surf at the simulator until they fall off the board. The facility is supervised by sports staff (safety, assistance, advice).
the Outdoor Youth Area will be transformed into the Splashaway Bay (kids water park).
Splashaway Bay (open between 8 am – 8 pm) is the kids-only aqua park. It has 2 whirlpools, 1 splash pool, 1 mini waterslide, interactive splash areas with multiple geysers and water cannons.