With the Nikon D750 being such a new camera, there is no waterproof case that comes with the model number etched on the outside. However, looking over the dimensions and position of the controls, we do believe there is a Nikon D750 underwater housing alternative for now, and that is the one that supports the D610.
This means that there is a Nikon D750 waterproof case support for divers, although they do not come cheap. Just so you know, the D610 case is the same as the D600 model, and no doubt it supports other models as well.
We have found five possible models that support the Nikon D750, with prices ranging from as little as $500, to almost $3,500, although a small price to pay for the sort of work or recreation use it will get.
The five models are the Aquatica AD600 Underwater DSLR Housing at $3,359.95, Ewa-Marine U-BXP100 Soft at $499.00, Ikelite Underwater case for $1,799.95, the Nauticam Underwater DSLR Housing at a cost of $3,300.00, and finally the Sea and Sea MDX-D600 model, which has a price of $2,699.95.
You can find details on these waterproof camera housings by visiting HousingCamera.com.