Actually this has been in discussion for a few years certainly in the Alaska and Pacific West Coast Market under the ' Northwest Ports Clean Air Strategy' protocols.
Per the UK boards I belong to, this is in place around the British Isles today and some ships take on this fuel outside the zone.
A lot of the newer ships use Gas Turbines / Electric and others Low Sulfur oil / Electric while some ports now are able to hook the ship up while in port to the local electrical grid. This was a joint venture with major cruise lines and the Port Authority and the Electrical Hydro providers.
Originally this all started because of emissions while in port also some ships have what is called scrubbers.
My UK board also reported a similar report a few days ago from the Globe and Mail.
Clean Fuel Rules May Prompt FO to Bypass Canada - Cruises.co.uk - SHOWTHREAD
The large cruise companies will adjust, are aware. I cannot see them reducing the market especially as the larger and new ships allow an economy of scale which exists per ship per passenger.
Much like full passenger planes or newer ones like A380