Most underwater housings equipped with fiber optic cables use the built-in flash of the camera to trigger the strobes. Ikelite DSLR housings for the Nikon SLR camera’s however use an electrical TTL circuit connected with the hot shoe that transmits the electrical signal via a bulk-head and sync cables to their strobes.
In these housings the Nikon pop-up flash cannot be used to trigger a fiber cable. The housing just doesn’t allow the flash to pop-up. Ikelite does sell an optical adapter that fires any of their strobes for housings fitted with fiber optic cables. But not for their own housings. Sea&Sea new MDX –D7100 housing does have this possibility for the Nikon D7100. And of course the new Nauticam D7100 housing. I wonder if Ikelite could not follow the same strategy? And offer their clients a (future) DSLR housing that provides both optical and electrical cable bulkheads. What you need first, is a small extension of top of the housing that doesn’t block the pop-up flash anymore..